Aṣl (pl. uṣūl), a term in the science of ḥadīth which signifies any primary written copy of ḥadīth which is derived directly from orally transmitted accounts. The word is used in different ways by Sunnis and Shiʿis. The term aṣl, in the sense of a source of transmission (maṣdar al-naql), has a history as old as ḥadīth narration and the science of ḥadīth itself. The ḥadīth original serves almost the same function as a compilation (muṣannaf), the only difference being that compilations were topically arranged (tadwīn) in some manner, which necessarily involved input from the write…