ḤADĪTH. The Arabic word ḥadīth literally means speech and also new: because speech is created as it is uttered, it is always new. Following Prophet Muḥammad's death (632 CE), people engaged in speech about him so much that the word ḥadīth was eventually reserved for speech related to the Prophet, including his own speech; it then came to refer to the sayings of the Prophet and his companions, and finally only to the sayings of the Prophet himself.

Sunnah (lit., a beaten track) is a parallel word to ḥadīth, as both refer to the speech and conduct of the Prophet, yet the two usages initially signified different shades of meaning. Ḥadīth denoted speech or word whereas sunnah signified actual conduct, or the way of doing something. It was, however, difficult to draw a...