“Sunna” (Arab. sunnah, “custom, way”) emerged as a central normative concept for Muslims within the first two centuries of Islam. While the Qur’an speaks of the “Sunna of God” and the “Sunna of the early generations,” Muslim scholars of the early period focused primarily on the Sunna of the Prophet Muḥammad (ca. 570–632). Many of these scholars went to great lengths to collect reports, called hadith (sing. and pl.; Arab. ḥadīth, “speech, report”), of his actions and statements and of the practices that received his tacit approval. Each hadith consists of a chain of authorities (isnād) a…