from a later consensus—whether after the age of the Successors or after the first three praiseworthy generations—even though the younger Successors lived into the third century. Whenever he spoke of the consensus of an age he was referring only to the generation of the Successors. In reality, his words were a warning against asserting an explicit, all-encompassing consensus. What he affirmed, as he said, was a tacit consensus, or the agreement of the majority when no opposing view is known. Thus, on the question of reciting behind the imam he said that consensus had been alleged concerning the occasion of revelation of the verse and concerning the non-obligation of recitation in audible prayers. It is the dialectical theologians, such as Bishr al-Marrīsī and al-Aṣamm, who speak of consensus while knowing little beyond the opinions of Abū Ḥanīfah, Mālik, and their likes, and who remain unaware of the positions of the Companions and the Successors.
More than one jurist—Mālik, Muḥammad ibn al-Ḥasan, al-Shāfiʿī, and Abū ʿUbayd—has claimed consensus in certain legal questions in which disagreement in fact existed but had not come to their attention.
Reliance upon the Book, the Sunnah, and consensus appears in the words of ʿUmar ibn al-Khaṭṭāb, ʿAbd Allāh ibn Masʿūd, and others, each of whom would say: “I judge according to the Book of Allah; if nothing is found there, then according to the Sunnah of the Messenger of Allah; and if nothing is found there, then according to what the righteous have unanimously agreed upon.” In another wording: “according to what the righteous have ruled,” and in yet another: “according to what people have unanimously decided.” The very fact that this recourse comes after the two principal sources shows that those righteous ones never opposed the Book and the Sunnah. (End of quote)
Al-Rāzī said in al-Maḥṣūl (4/23): “Some concede that such unanimity is conceivably possible, yet they contend that we have no way of knowing for certain that it has occurred. Knowledge of things is either immediate (wijdānī) or not. Immediate knowledge is what each of us feels of hunger, thirst, pleasure, pain, and the like; obviously, knowing that the whole community of Muhammad ﷺ has agreed on a matter is not of that category. As for knowledge that is not immediate, they agree that the means to it is either sensory perception, transmitted report, or rational inference. Rational inference has no scope here for determining whether a given individual held a certain view or not; the remaining routes are perception and report. But it is clear that hearing someone’s statement, or being informed of it, is impossible without first identifying that person; therefore certainty about the community’s consensus cannot be attained unless every single member of the community is known—and that is categorically impossible. Hence…”