first recognized by Abu Yusuf (d. 182/798), an early leader of the Hanafi school, though it was considered part of the , i.e genuine and not a formal source. Later al-Sarakhsi (d. 483/1090) opposed it, holding that custom cannot prevail over a written text.

;Scriptural basisThe idea that custom is an authoritative source for Islamic law appears in the Quran and Hadith. One hadith narrated by Ibn Mas'ud