An Arabic treatise by the Damascene physician, ethicist, and legalist Ibn Ayyūb al-Qādiri (d. 1463) survives in only a single manuscript (CBL AR 5162) yet documents the substantial professional esteem late-Mamluk scholars accorded knowledge of medicine and the natural sciences. Written in the early-fifteenth century and entitled Preventing the Harm Caused by Teaching Causal Efficacy, al-Qādirī describes his work as “an exercise for students of the natural sciences, though teaching certain of its doctrines is discouraged.” Here thereby situates his text within a medieval Islamic intellectual controversy over the reality of causality and contagious disease. Scholarship of the twentieth century characterized Muslim intellectuals of this period as rejecting the concepts outright in favor of occasionalism, or the theological position that God individually determines the course of all events such that the direct causality inherent to occurrences like the outbreak of contagious disease must be rejected. Using this overlooked manuscript I argue that the subject was in fact understood with far greater nuance by some scholars of the fifteenth century, whose criticisms of contagion were motivated less by its lack of logical demonstration and more by the clinical observation and theorization of physicians. This is certainly true of al-Qādirī’s treatise, which he presents as a guide for lay scholars and apprentice physicians alike, as well as a reasoned meditation on the multiple benefits and hard limits of the sciences in the premodern era. Indeed, the text discusses topics that range from the logical bases for contagion and causality to extended passages on scholarly sexuality, diet, and self-care. A more sustained analysis of this digest alongside better studied treatises on the topic will shed much needed light on a medieval controversy of immediate relevance. It will likewise bring modern scholarship beyond assertions of the medieval ulema’s religious motives, and toward an appreciation for the robust intellectual standards of their scholarly society.