Founded in Cairo in the year 797/1395, the Maḥmūdīyah Library would become the largest public library in 9th/15th century Mamluk Egypt. Studies on Islamic manuscript libraries have only mentioned this important institution in passing based on what little can be gleaned from the narrative sources. However, these studies have neglected the wealth of information available on the numerous surviving manuscripts from this library now scattered in collections around the world. By analyzing various notes on this manuscript corpus and corroborating my findings with archival and narrative sources, I show the more sordid history behind the creation of this madrasa library. A story emerges of Maḥmūd al-Ustādār, a corrupt emir in the Mamluk administration who, despite his innocuous claim to wish to create a library “for the students of the noble science [of ḥadīth] to benefit from”, was also motivated to by a desire to protect his books from being confiscated by the sultan Barqūq shortly before his arrest. Tracing the circulation history of the Maḥmūdīyah corpus further back, I show how this Maḥmūd had seized these books from the inheritance left to the orphaned son of the former Grand Shāfiʿī Judge of Egypt Burhān al-Dīn Ibrāhīm ibn Jamāʿah. Finally, by looking at some earlier notes on the manuscript corpus, I offer some reasons why the judge Ibrāhīm ibn Jamāʿah had collected these specific books over the course of his life before they passed on to his son, then the emir Maḥmūd, and finally the shelves of the Maḥmūdīyah Library. This paper contributes to our understanding of religious endowment practices in the Mamluk period as well as the field of book culture in the manuscript age, showing the often hazy boundary between the concept of public and private ownership of books. It also invites future researchers to consider the value of paratextual data on Islamic manuscripts as a rich source for social, intellectual, and institutional history.