Establishing the Sunnah’s attribution to the Prophet (peace and blessings be upon him) concerns hadith alone, for the Quran has been conveyed to us through unequivocal, successive mass transmission—both in wording and meaning—handed down from the younger to the elder generations, so it needs no investigation as to its authenticity.

Know, then, that the science of hadith is divided into two branches:

1 – ʿilm al-ḥadīth riwāyah (the study of hadith transmission).
2 – ʿilm al-ḥadīth dirāyah (the study of hadith critique).

ʿIlm al-ḥadīth riwāyah investigates whatever is transmitted from the Prophet—his statements, actions, and states—and it focuses on what is transmitted, not on the act of transmission itself. For example, when a report reaches us from the Prophet (peace and blessings be upon him) we ask: Is it a statement, an action, or a state? Does it indicate a particular ruling or not? Such inquiry is the essence of riwāyah. Its subject matter is the very person of the Prophet (peace and blessings be upon him) and whatever proceeds from him in the form of words, deeds, or states. Among those deeds is tacit approval, which counts as an action, while his states include qualities such as height or shortness, complexion, anger, joy, and the like.

As for ʿilm al-ḥadīth dirāyah, it is the discipline that examines the conditions of both the narrator and what is narrated, determining whether they are to be accepted or rejected. For instance, when we find a narrator, we investigate whether that narrator is acceptable or rejected; likewise, with the narrated report we examine which parts are admissible and which are to be discarded. From this we learn that accepting a narrator does not necessarily entail accepting what he narrates, for a chain may be composed of reliable, upright transmitters, yet the text itself may be anomalous or harbor a hidden defect, in which case we do not accept it. Conversely, there are occasions when the men of the chain do not rise to the level of acceptance.