This article contributes to Islamicist scholarship on the relationship between modern technology and Muslim thought and practice by closely reading and historicizing a twentieth-century South Asian Ḥanafī treatise on the use of the loudspeaker in ritual prayers. In this treatise, the Ḥanafī jurist Muḥammad Shafīʿ discusses the reasons for changing his legal opinion. The jurist first argued that the use of the loudspeaker invalidates the ritual prayer of the congregant (muqtadī). In his revised position, however, he held that the loudspeaker should be avoided in ritual prayers, but that its use does not invalidate the prayer. While Muḥammad Shafīʿ appears to have revised his position in response to newfound scientific knowledge about the ontological status of the loudspeaker’s sound or for the sake of public benefit (maṣlaḥah), I suggest that his revised fatwā was based on distinctive Ḥanafī modes of legal reasoning. By grounding his revised position in casuistry, the muftī renewed his commitment to his law school’s methodologies in a social context in which scientific knowledge and legal pluralism were weakening Ḥanafī modes of reasoning.