1 Introduction

Waqf is a crucial Islamic social finance tool. Waqf is essentially seen as a trust of an asset that generates income for the benefit of specific groups or individuals (El Khatib 2016). These charities' recurring nature is often considered the stepping stone for Waqf development in Islam (Abdel Mohsin 2009). Otherwise, similar charitable activities, such as zakat, have been cited in academic literature having a profound impact from individual and commercial standpoints (Hassan and Rashid 2017; Ahmad et al. 2015; Rashid et al. 2017). While the zakat fund is restricted to be used for certain groups of recipients, in general, the payment of Waqf for the benefits of Muslims and non-Muslims is allowed.

Contributions of the Waqf fund can be distributed for the causes of not only religious, such as building places of worships or financing the expenses during the war, but also for the general socio-economic needs of all sorts, such as establishing schools, developing infrastructure, the welfare of the poor, and sustainable entrepreneurship activities (Al-Gebori and Humaish 2008; Hasan et al. 2018; Hasan et al. 2019a, 2019b). However, due to the perpetual nature of the asset under Waqf, apart from the legal challenges, other difficulties with Waqf grossly include the management aspect of the asset. As such, past researchers have embarked on the journey to explore the ability of Waqf to bring socio-economic changes in poverty-stricken emerging economies (Sadeq 2002; Mohsin 2013).

After a brief review of existing studies on Waqf, we find that past researchers have covered Waqf from various dimensions. We find waqf studies covering legal (Kuran 2001), economic (Sadeq 2002), social (Douman 1998), financial (Mohsin 2013), and accounting issues (Yatla 2011). Although research issues in Waqf have evolved from the general aspect of Waqf (Jurist 1914), recent studies are focusing on transparency and governance among waqf institutions (Hasan et al. 2017). Research interest in Waqf is growing (see Table 2), which motivates this study to conduct a bibliometric review of past waqf literature with a specific objective to classify past waqf literature into study themes, highlight gaps and propose future research directions.

This study extends on this pursuit of identifying, categorizing, and analyzing a comprehensive list of tasks on Waqf using bibliometric analysis. The research will identify influential topics, significant dimensions of research, and impactful researchers across several periods in a nutshell. In this study, we extracted relevant publications using the Scopus database that included a post-filtered final sample of 319 research publications from 1914 until 2020. Our selection included both journal articles and reviews. We employed R-Studio, VOSviewer, and Microsoft Excel for citation analysis, content, and network analyses. Given the importance of Waqf studies, we covered the most extensive indexed collection of documents available on Waqf.

The review resulted in four major dimensions of Waqf's research. These are: (1) Cash Waqf endowment, (2) Islamic accountability and Waqf, (3) Waqf and Islamic social Finance, and (4) Governance for Waqf endowment. Cash Waqf stood out of the crowd as the most cited topic. Overall, the number of researches on Waqf increased at a rate of 9.27% annually. Malaysian researchers contributed the most to scholarly works (155 out of 319), followed by researchers from Indonesia, the United States, the United Kingdom, and Germany in the top five. We supplemented our findings with Bradford's Law, bibliographical coupling, co-citation analysis, cartography, and several content analyses.

Our analyses yield three critical conclusions. Firstly, cash Waqf has been investigated the highest number of times, indicating its popularity to expand the boundaries of traditional Waqf. The apparent etiology behind the growing attention to cash Waqf appears from specific inherent characteristics of the cash Waqf system. These include flexibility, diversity of the usage, and convenience of managing the fund or trust compared to the legal complexities associated with the real estate Waqf. Secondly, the geographic penetration of the research on Waqf has crossed the boundary of religious practices. Aside from Malaysia and Indonesia, Waqf has been discussed as a valuable economic tool in the United Kingdom, the United States, and Israel, among many. Even though applying the common law in these non-Muslim-dominant countries is to be adjusted for the inclusion of Waqf, increasing practice at the individual level rightfully seeks more scholarly and professional attention. Thirdly, Waqf has its tremendous benefit via connecting poverty, sustainability, and social welfare to ensure socio-economic justice. Researchers have reported Waqf to help reduce socio-economic inequality. Future research, thus, can be expanded into several areas, including law, management, economics, finance, and Islamic studies.

We discuss the methodology in Sect. 2. Next, results are presented in Sect. 3. Section 4 provides the results of content analysis of selected literature for an in-depth review of the results from Sect. 3. Finally, Sect. 5 concludes the study with a summary of the findings and implications for future research.

2 Methodology

This study employed a bibliometric method to produce quantitative results on Waqf literature. Bibliometric analysis, combined with content analysis, is becoming increasingly popular among scholars (Koskinen et al. 2008). To ensure reliability and validity, descriptive, integrative, systematic, or meta-analytic reviews are combined with bibliometric review to provide the quantitative aspect of the literature (Martínez-Climent et al. 2018). Nonetheless, bibliometric analysis, on its merit, is an emerging method with rare Islamic finance applications (Alshater et al. 2020). Moreover, the method can be differentiated from other comparable review techniques on the level of an in-depth and insightful key aspect of the phenomenon of interest.

2.1 Study design

We employed a three-stage methodological process (Fig. 1), which has been modified for this study from Paltrinieri et al. (2019). Paltrinieri et al. (2019) adopt an innovative approach in conducting a meta-literature review of Sukuk literature. The first step involves examining recognized databases to find relevant publications for meta-literature review. The second step of the literature review process begins with a quali-quanti approach that uses bibliometric citation analysis and content analysis to group existing studies in meaningful groups. Finally, Paltrinieri et al. (2019) apply co-citation, co-authorship, and cartography analysis to provide an in-depth analysis of past studies on Sukuk.

Fig. 1
figure 1

Research approach

Full size image

Following Paltrinieri et al. (2019), we relied on the Scopus database to collect our data. Scopus, owned by Elsevier, is a well-known publisher for -high-quality content. It is the most recognizable and widely used database for rigorous scientific production. Essentially, while maintaining the expected level of quality, we sacrificed the coverage since the selected database will not cover the literature universe on the phenomenon of interest. While the Web of Science (WOS) collection often supersedes the quality of the Scopus collection, the limitation on the coverage of the literature remain.

On the other hand, sourcing literature based on Google Scholar might be criticized for its quality and coverage. Hence, Scopus fits rightly in the middle and is convenient for the researcher. Table 1 shows the categorization of our journals based on the three comparative sources: WOS, Scopus, and Google Scholar.

Table 1 Categorization of the literature sources
Full size table

Before going to the search functions using Scopus, we conducted a brief brainstorming session with experts to identify the keywords that are to be efficient and convenient for our task. Next, we conducted a simple keyword analysis of the literature using Scopus engine search refinement options. The brainstorming session was crucial as we could easily match the keywords from the literature with those from the experts. This has contributed significantly to the validity of the search. Table 2 shows the keywords used in the investigation.

Table 2 Search keywords and the number of manuscripts
Full size table

Researcher intervention is often needed to clear manuscripts from selection if those are not matching with the study's objectives. For example, more than 20 studies were tackling Waqf Aswan, a mountain in Jordan, which geologists studied for several reasons and did not relate to the Waqf literature of our interest. After filtering, our search efforts finally delivered 319 articles and review manuscripts. Our selection portrays a higher level of inclusion from various aspects. To point out two such uniqueness: Firstly, the data covers the most extended period of studies for almost 100 years ranging from 1914 until 2020.Footnote 1 Secondly, after manual cleaning of the data by a cursory examination of each paper to confirm or reject its relevancy to our topic, 319 articles and reviews remained. These are the total number of Waqf literature directly connected to Islamic Finance and accounting. Hence, the study is the first to consider the entire population of the Waqf literature. This data was analyzed based on various tests to answer our research question. Section 2.3 will discuss these analyses. In the appendix, we report a list of literature for the top 10 cited articles on Waqf to complement the bibliometric analysis. It is the belief that the general classifications for the articles and a literature review for each topic are helpful for researchers to get a bird view of the literature, purpose, findings, and methodology of the area of research.

3 Tools of analysis

We use three bibliometric analysis tools: RStudio, VOSviewer, and Excel. RStudio is widely used to generate bibliographical data for the dataset. VOSviewer was used to perform network and content analysis. VOSviewer enables the users to create and visualize bibliometric networks (Van Eck and Waltman 2013). These visualizations are often called maps used to perform various network analyses, such as the co-authorship, co-occurrence, and co-citations. This relationship network can be constructed for authors, sources, countries, and keywords. VOSviewer was also used to perform bibliographical coupling. We used Microsoft Excel to complement RStudio, as the graphs from the latter were not easily editable as it was done using Excel.

3.1 Type of analysis

The analyses progressed in three folds. Firstly, we performed a general performance analysis. This section extracted public info about the dataset and the literature growth over the years. We also addressed critical aspects of the literature, such as the most relevant authors, their base countries, and affiliations. We performed an analysis using Bradford's Law to address the key sources. Secondly, we performed a citation analysis. This section addressed the most cited documents, references, and sources, together with the sources and authors' impact. Thirdly, we performed a network and content analysis using the bibliographical coupling, co-citation, and co-occurrence analysis. Finally, we employed the hierarchical analysis (dendrogram) to ensure the most accurate clustering.

4 Results and discussion

Table 3 provides a general overview of the collected data of 319 articles spanned over 100 years. This number includes 278 journal articles with an average of 7.27 citations per year and 4.52 citations per document. From 581, around 63% of the papers were co-authored. The review covered a total of 736 keywords.

Table 3 Summary of the review
Full size table

Figure 2 shows the -year-wise distribution of the 319 papers published between 1914 and June 2020. With an annual growth rate of 9.27%, there is a clear indication of Waqf being an interesting topic since the year 2000 and onward.

Fig. 2
figure 2

Document Growth by year

Full size image

4.1 Most influential authors, affiliations, and countries

The growth of articles in this field was associated with the scientific community of authors, sources, and affiliations. Figure 3 shows the most relevant authors on this topic. Mohammed is the most impactful researcher with eight published articles, followed by Johari, Orabay, and Sabri, each having five published articles to their credit. The net ten authors had four published articles each.

Fig. 3
figure 3

Most relevant authors in Waqf literature

Full size image

Figure 4 presents nine out of the top ten affiliated institutions located in Malaysia. This is due to being a hub for Islamic finance education. International Islamic University Malaysia (IIUM), a dedicated center for islamic finance education, comes first in the race to publish the highest number of articles in Waqf. We also identified five papers from Indonesia in the top ten list of affiliations. Figure 5 shows that around 49% of the authors of the published documents were affiliated with a Malaysian institution.

Fig. 4
figure 4

Most relative affiliations

Full size image
Fig. 5
figure 5

Most relevant countries

Full size image

Bradford's law estimates the exponentially diminishing returns of searching for references in journals. One formulation is that if several articles sort journals in a field into three groups, each with about one-third of all articles, then the number of journals in each group will be proportional to 1:n:n2 (B.C. 1948). Thus, Fig. 6 shows that 'Journal of the Economic and Social History of The Orient’ is the first by leaps from the second journal 'Intellectual Discourse,' followed by 'Journal of King Abdulaziz University for Islamic Economics.'

Fig. 6
figure 6

Bradford's Law

Full size image

4.2 Citation analysis

Citation analysis states the connection between two documents. This analysis has been criticized for mispresenting the quality evaluation of a paper due to negative citations (citation of incorrect results), self-citations, and neglecting the time frame given for citations, among others (Seglen 1989). Despite these criticisms, citation analysis is still a worthy indicator of influence (Garfield 1979). This section provides citation analysis of the documents, references, and sources alongside the impact of sources and authors. Table 4 addresses the most cited papers of Waqf literature. About the citation analysis, Table 5 addresses the most local cited references, Table 6 and Table 7 address authors' and sources' impact, respectively. While 'Law and Society' received the highest citations of a single paper, 'Journal of the Economic and Social History of The Orient' reported the highest impact.

Table 4 Top ten cited global documents
Full size table
Table 5 Top ten most locally and globally cited references
Full size table
Table 6 Authors' impact
Full size table
Table 7 Sources' impact
Full size table

We notice no significant reference dominating part of the literature, maybe except the first reference by Sadeq Am, published in Int. J of Soc. Economics. Table 6 provides the authors' impact inside Waqf again; again, no significant author is dominating from the intellectual side in this topic. Concerning the source impact, we notice that the journal of the economic and social history of the orient and intellectual discourse are the most relevant journals on this topic.

4.3 Network analysis

  1. (a)

    Bibliographical coupling

    We conduct citation mapping for the 319 Waqf articles using the bibliographic coupling technique in the VOSviewer software. VOSviewer allows three types of bibliographic coupling analysis, one each for journals, publications, and authors. Following van Eck and Waltman (2018), we set the unit of analysis to be 'document' and the method of analysis to be 'fractional analysis' during the bibliographic coupling analysis. The document counting method is set for fractional counting instead of the whole counting method. Fractional counting allows some level of control to minimize the influence of documents with a higher number of authors during the bibliometric review process. The minimum number of a citation for a paper is set to 5, and we also set the minimum value of clustering to 10 to identify meaningful clusters. This parameter resulted in identifying 56 papers out of the original 319 papers. Figure 7 provides the results generated from the bibliographic coupling analysis from VOSviewer. We identified four clusters. In Fig. 7, we identify 'cluster 1' in red, including 19 papers. We present 'cluster 2' in green with 14 papers, 'cluster 3' in blue with 11 papers, and 'cluster 4' in yellow with ten items. After reviewing the papers grouped in each cluster, we identify that clusters 1, 2, 3, and 4 discuss the application of Waqf for socio-economic development, accounting, and accountability issues, historical developments, Islamic social financing aspect of Waqf, respectively.

    Fig. 7
    figure 7

    Bibliographic coupling of 319 Waqf articles

    Full size image
  2. (b)

    Co-citation analysis

    In the next stage, we conduct a co-citation analysis using the source of the documents to visualize the network between the journals publishing Waqf-related papers. Co-citation analysis demonstrates the relatedness and interconnection among research articles and topics (Kim and McMillan 2008). The links provided in Fig. 8 indicate their relatedness. We set the minimum citation limit to 10, archiving 77 articles in five clusters. The general rule of thumb is that closely related journals are positioned near the co-citation figure generated by the VOSviewer. The current position of five clusters identified from the co-citation analysis reveals that Waqf papers being published in different journals are citing related papers, which have resulted in close links between the sources. Figure 8 allows us to explore the relatedness of the journals. In general, journals within proximity have more substantial relatedness, and lines also represent the stronger co-citation links. We find that the papers grouped in each cluster are closely linked by relevant co-citation and indicate the significance of papers published in various issues of Waqf (Shah et al. 2019).

    Fig. 8
    figure 8

    Co-citation of journals

    Full size image
  3. (c)

    Co-authorship

    We conduct further exploration of our clusters by examining the results on co-authorship using the fractional counting method. The purpose of using fractional counting is to reduce the influence of documents with many authors. We perform two separate co-authorship analyses. First, we perform co-authorship analysis using the country as a unit of study. Second, a minimum number of documents of a country and the minimum number of citations is set to '1' for a comprehensive analysis of the origins of the source documents. Such parameters result in the selection of 32 articles grouped into five clusters.

    Figure 9 provides the co-authorship analysis results using authors as a unit of analysis. We have set similar criteria applied while the country was the unit of analysis as shown in Fig. 10. A total number of 29 papers are reported in 5 clusters.

    Fig. 9
    figure 9

    Co-authorship by author

    Full size image
    Fig. 10
    figure 10

    Co-authorship by countries

    Full size image
  4. (d)

    Cartography analysis

    We found conflicting results from the co-authorship analysis. While the bibliographic coupling revealed four clusters, both co-citation and co-authorship results indicate the possibility of five clusters for the 319 Waqf papers selected for the bibliometric review. Therefore, we perform the cartography analysis to characterize the underlying research themes based on the keywords of the articles. Figure 11 presents the results of the cartography analysis from VOSviewer. We select co-occurrence as a method of analysis and choose all keywords as the unit of analysis. The minimum number of citations is set to '3'. We found four primary clusters for the 22 papers. The clusters are represented in 'red,' 'blue,' 'green' and 'yellow.' We report the keywords and the number of occurrences along with the link strength in Table 8. The link strength is a measure of the power of the link between items. We find the three most occurring keywords are Waqf, cash Waqf, and Islamic Finance.

    Fig. 11
    figure 11

    Keyword co-occurrence

    Full size image

    The cartography analysis using the co-occurrence method allows us to finalize the clusters and identify the key themes of the most frequently published Waqf papers. We find that the first cluster is related to cash Waqf. Cash Waqf's publication has expanded to various sub-themes. However, the most common theme of cash Waqf research is related to economic and sustainable development. The second cluster identifies one of the contemporary themes of Waqf literature which focuses on the accountability issue. In the third cluster, we group cash Waqf papers focusing on Islamic social Finance to reduce inequality and promote entrepreneurship. This cluster has several sub-themes, including charitable instruments in Islam and the effectiveness of Waqf as a charitable vehicle for social development. Finally, the fourth cluster focuses on the governance issues related to cash Waqf.

    Based on the above analysis, we finalize four clusters to study 319 Waqf papers. Detailed discussion on the research agenda is discussed in the next section, followed by future research directions.

Table 8 Keywords and the number of occurrences along with the link strength
Full size table

5 Content analysis and research agenda

5.1 Research streams

  1. (a)

    Research Stream 1: Cash Waqf endowments for sustainable development

    The first research stream focuses on cash Waqf endowments and their role in sustainable development. The concept of sustainable development is diverse. However, we find that most of the authors have focused on the role of cash Waqf on poverty alleviation through microfinance schemes. Thaker (2018), for example, introduces a cash Waqf model that could finance the ventures of micro-enterprises. The conceptual model is developed from expert opinions and covers regulatory issues, governance, and public awareness. Abd Rahman and Awang (2018) complement the theoretical model of Thaker (2018) by providing a critical analysis of cash Waqf implementation in the context of Malaysia. We find the type of cash Waqf approved by the jurists and various challenges in implementing cash Waqf in Malaysia from the study of Abd Rahman and Awang (2018). However, we find a considerable difference between the models proposed by Kachkar (2017) and Thaker (2018).

    While the model by Thaker (2018) focuses on the funding source of micro-enterprises, Kachkar (2017) develops a cash Waqf model for a specific group of users, more specifically, refugees. The conceptual model of cash Waqf proposed by Hassan et al. (2018) contributes to the literature by introducing the role of alternative markets and institutions in cash Waqf from a multi-country perspective. Our critical review of this research stream on cash Waqf studies indicates a growing trend of conceptual model development that can integrate cash Waqf into sustainable development strategies. However, we find limited empirical evidence on the practical application of these conceptual models. The study of Hasan et al. (2019a, b) makes a unique contribution by providing empirical evidence on the importance of building trust among donors for Waqf institutions. Findings provided by Hasan et al. (2019a, b) are valuable for both Waqf managers and regulators due to Waqf contribution's voluntary nature compared to zakat. Therefore, we also identify the need to apply unique research methods to explore the complex role of cash Waqf in sustainable development.

  2. (b)

    Research Stream 2: Implications of Islamic accountability for Waqf

    The growing demand for accountability issues in Islamic Finance is captured in the second research stream. We identify several influential papers on Waqf that cover accountability from an Islamic perspective. Ihsan et al. (2016) provide a historical perspective on the development of the Islamic accountability concept. Their work is significant as it starts from the broader definition of accountability and progresses toward Islamic accountability. Also, Ihsan et al. (2016) specify various measures to discharge Islamic accountability. Siswantoro et al. (2018) refine the efforts prescribed by Ihsan et al. (2016). However, Siswantoro et al. (2018) only focus on cash Waqf institutions in Indonesia.

    Ayedh et al. (2018) contribute by providing empirical evidence on the extent and mode preferred by mutawatir to discharge their accountability to the stakeholders. Their study identifies the key stakeholders and discusses the driving force of Waqf accountability. Ayedh et al. (2018) find that mutawallis show upward accountability instead of downward accountability. We find a detailed discussion on upward and downward accountability in Ahmad and Hasan (2017), where upward accountability is first linked to the spiritual dimension where the pleasure of Almighty Allah is the ultimate goal, and all stakeholders of Waqf are accountable to Him. In the next phase, mutawallis are accountable to waqif (donor or fund providers). Finally, the secondary accountability of Waqf managers covers the secular dimension and relates to the beneficiaries, regulatory agencies, and the general public. Therefore, the findings of Ayedh et al. (2018) complement the conceptual model of Ahmad and Hasan (2017) by specifying the importance of a specific type of accountability for mutawallis. However, Osman and Agyemang (2020) indicate the need for downward accountability for Waqf management. Such diverse findings pave the way for future research on the role of accountability in Waqf management.

  3. (c)

    Research Stream 3: Islamic Social finance through Waqf

    We have discussed the role of cash Waqf in sustainable development. The third research stream differs from the research stream. First, it covers the broader applications of Waqf funds. Second, the role of Waqf as a tool for social Finance is covered in this research stream as opposed to the sustainability dimension in the first research stream. Mohammad (2015) promotes the need for developing an Islamic social bank based on the concept of Waqf as an alternative to the current banking system. The author builds the idea of Islamic social banks on the theoretical perspective of Waqf as a tool for sustainable poverty eradication tool. Abduh (2019) further establishes the role of Waqf based on Islamic social Finance in financial inclusion.

    Uddin and Mohiuddin (2020) tackle the regulatory constraints of implementing a Waqf-based Islamic social finance model in an emerging country such a Bangladesh. They identify three challenges of Islamic social Finance based on the Waqf concept: lack of government support, complex regulatory environment, and institutional standardization. Jouti (2019) also proposes an integrated approach to build a sustainable Islamic social finance ecosystem. One of the unique aspects of Jouti (2019) study is the interlink of various Islamic institutions as support institutions for Waqf in the Islamic ecosystem. Also, we find that the concept of crowdfunding is integrated into the conceptual Islamic ecosystem proposed by Jouti (2019), which is absent in other conceptual models.

  4. (d)

    Research Stream 4: Good governance for Islamic endowment

    In the final research stream, we identify one of the contemporary issues in Waqf literature. Research stream four covers governance issues relevant to Waqf institutions. Hassan et al. (2017) contribute to the literature by specifying the best Shariah governance practices for Waqf institutions. Hassan et al. (2017) proposed the best Shariah governance framework thus far covers the concept of trustworthiness, accountability, God-consciousness, Hisbah, and mutual consultation in decision making. Daud (2019) focuses on the role of Islamic governance in Waqf reporting and contributes by establishing good governance in transparent reporting practices. Such findings complement the findings of Hasan et al. (2017), where the role of governance on transparent reporting is discussed from a theoretical perspective. Hasan et al. (2017) also introduced the board's role in building trust among stakeholders through transparent reporting. Mohd. Zain et al. (2018) extend Waqf's governance discussion by covering the internal control aspects. Their study covers five key areas of internal control, including control environment, risk assessment, control activities, transparent communication and monitoring, and recommendations for evaluating the internal control system and adopting the Wasatiyyah approach. According to Shariah standards, the Wasatiyah approach concentrates on justice, excellence, and balance, which can improve the operation of the Waqf institution.

5.2 Research agenda

We extend our discussion on the research clusters in this section and explore the relevant research agenda. We identified several research gaps through our bibliometric literature review process, which paves the way for future Waqf research. First, in the cash Waqf research cluster, we find that majority of the cash Waqf models of sustainable development proposed by authors are conceptual. There is minimal empirical evidence on the practical application of such models for sustainable development. As a result, we could not find generalizable findings linked with the diverse nature of cash Waqf implementation across emerging countries. Second, in the Islamic accountability research cluster, we find various modes of discharging Islamic accountability among Waqf institutions. There is a need for extensive conceptual and empirical analysis to establish a uniform Islamic accountability framework for Waqf institutions. Third, in cluster three, we focus primarily on Islamic social Finance through Waqf endowments. While past studies propose conceptual models integrative various Islamic finance instruments, we rarely find empirical evidence that explains the willingness of Waqf institutions to participate in the Islamic social finance ecosystem. Fourth, we find a limited number of studies focusing on the importance of digitalization to revive Waqf as an Islamic social finance platform. Finally, we identify good governance as one of the critical research clusters in Waqf. In recent years, we find discussion on governance and its role in improving reporting for waqf institutions. Future research can focus on the factors determining the extent of voluntary waqf reporting. Also, there is a need to develop a good governance framework for waqf institutions. We summarize the research gaps and future research agenda in Table 9.

Table 9 Research gap and future research agenda
Full size table

6 Conclusion

Due to its significant contributions to sustainable socio-economic development in Muslim and non-Muslim-dominant societies, Waqf has received considerable attention globally. The objective of this study was to present a systematic review of Waqf literature. We have employed bibliometric and thematic reviews to address the objectives. The objectives can be sub-divided into three outcomes. Firstly, we identify and discuss the bibliometric status of waqf literature. We have employed R-studio to conduct bibliometric reviews on 319 documents listed on the Scopus database. Important demographic details of the reviewed studies present that most studies were conducted using Malaysia and Indonesia.

Interestingly, studies by authors from the United States, United Kingdom, and even Israel also received significant attention in repeated citation analysis. Published papers give a strong sense of collective and collaborative research among researchers, even though they promote diverse geographic locations. This collaboration also implies a common tendency to relate Waqf practices to the Islamic Shariah. From the scientometric aspect, we found that The Journal of the Economic and Social History of the Orient (JESHO) and Intellectual Discourse were the most relevant journals on Waqf. Most influential authors (i.e., Mohammed Mo and Johari F., etc.) were primarily affiliated with Malaysian higher education institutions, such as IIUM, UKM, USM, and UM. Reviews also revealed that a significant portion of the studies took cash Waqf as their primary topic of interest.

Secondly, the study forwards four significant themes of waqf research. These themes are 1) cash waqf endowment for sustainable development, 2) implications of Islamic accountability for Waqf, 3) Islamic social finance through Waqf, and 4) good governance for Islamic endowment. Due to the globalization of the Islamic financial markets, the implications of cash Waqf are expected to expand the horizon of relevant research. Thirdly, we discuss several research topics/ questions for future research. We forward this view that future studies on Waqf will concentrate on cash Waqf with its connections to instruments offering sustainable economic efficiency. The role of the Waqf institution, trust in the Waqf management system, and convenience of using the system, in general, may have a significant influence on researchers' choice of topics soon. The role of allied Islamic social finance institutions, such as the zakat or Islamic microcredit, can be debated. However, as the research on Waqf is intertwined with research on other similar institutions, the possibility of integrated Islamic social institutions is highly plausible. Other areas of prospective interest may include establishing a governance and disclosure framework for Waqf institutions. Finally, there remains a strong need for higher quality quantitative modeling relating to the contributions of Waqf on economic development, social inclusion, entrepreneurship, inequality, and other related parameters.