This paper explores how a Transoxanian Muslim scholar of the 6th century AH/12th century CE, Najm al-Din 'Umar al-Nasafi, constructed an Islamic theory of knowledge which gave theoretical grounding to the validity of the Qur'an as the word of God and statements from and about the Prophet Muhammad (the hadith). This epistemology is exemplified by the development of the theory of akhbar - or testimony - and in particular, the concept tawatur, or recurrent transmission. Combining evidence from al-Nasafi's well-known treatise of Islamic theology, al-Aqa'id al-Nasafiyya, with new material from his unstudied work of Islamic legal theory, Tahsil Usul al-Fiqh, I argue that the theory of akhbar articulated between these two works and two disciplines not only demonstrates the shared epistemology of these fields, but also reflects communitarian rather than individualistic epistemic commitments, highlighting the consequences of positing epistemology as a communal boundary. Tawatur is a concept which describes the transmission of a report by a sufficient number of agents over time and space so as to preclude error or agreement on a lie, and guarantees knowledge for the recipient of the report. Considering the relative dearth in scholarship on Islamic approaches to sources of knowledge such as testimony/tawatur, and the importance of introducing an unstudied work of Islamic legal theory by one of the most celebrated intellectuals of the Hanafi legal school, my paper aims to expand on a method for better understanding Islamic approaches to epistemology, while providing some sense of what the Tahsil brings to the field. As Martin Kusch has proposed in his theory of communitarian epistemology, communities generate knowledge through testimony, which is itself a social agreement that contributes to the constitution of social institutions. I have found a similar approach to testimony in the work of al-Nasafi, in that the knowledge arrived at by akhbar is generated, and through wide distribution and constant performance (that is, transmission), maintains certain social institutions such as the Qur'an and the hadith. This paper demonstrates that in al-Nasafi's theory, multiple, intersecting communities can participate in the maintenance of these social institutions through testimony, and that this multiplicity posed a significant challenge for Muslim scholars: that is, a general claim that the agreement of communities on a belief (through testimony) is dispositive would allow for the acceptance of otherwise false beliefs in Islamic epistemology.