The point, then, is that when a lengthy report is transmitted, for example, through two distinct routes with no collusion between them, it becomes as impossible for it to be mistaken as it is for it to be fabricated.

Indeed, the vast majority of what is found in the collections of al-Bukhari and Muslim belongs to this category—reports about which one can be certain that the Prophet (peace and blessings be upon him) actually said them.

For that reason the great mass of scholars, across every school, hold that a solitary report which the Muslim community has received with acceptance—either by affirming its content or by acting upon it—yields certain knowledge.

Just as the scholars adduce and make use of a narration whose transmitter is prone to poor memory, they likewise declare portions of a hadith transmitted by a trustworthy, upright, and precise narrator to be weak once evidence shows that he erred in those parts. They arrive at such conclusions by means of various indicators, calling this discipline the “science of hadith defects (ʿilal),” one of the most noble branches of their learning.

People in this field have fallen into two extremes. One group, made up of speculative theologians and the like, is far removed from knowledge of hadith and its specialists; unable to distinguish sound from weak reports, they fall into doubt about the authenticity of narrations—or about the certainty one can have regarding them—even though such reports are well-established and decisive among the hadith scholars. The other extreme consists of those who claim to follow the hadith and act upon it: whenever they find a wording in a narration transmitted by a trustworthy narrator, or they encounter a chain whose outward appearance seems sound, they wish to place it on the same level as those reports whose authenticity the experts have decisively affirmed. Then, when that narration conflicts with a well-known authentic hadith, they resort to contrived and feeble interpretations or treat it as a proof in doctrinal and legal issues, even though the hadith specialists know that such a procedure is erroneous. Just as a hadith bears indicators by which one can know—and even be certain—that it is true, it likewise carries signs by which one can know, with equal certainty, that it is false.