Mālik, and that is likewise the position of Abū Ḥanīfah and his disciples. Abū Yūsuf—may Allah have mercy on him—the foremost pupil of Abū Ḥanīfah and the first to be styled “Chief Judge,” met Mālik and asked him about these issues. When Mālik replied by citing the mass-transmitted (mutawātir) practice of the people of Medina, Abū Yūsuf retracted his earlier view and said, “Had my teacher seen what I have seen, he would have retracted just as I have.” Abū Yūsuf thus reported that this kind of transmission is regarded as proof by his teacher Abū Ḥanīfah just as it is by others. The only reason Abū Ḥanīfah did not adopt it is that the report never reached him—just as many ḥadīths failed to reach him and other leading Imams. They therefore deserve no blame for omitting what had not come to their knowledge.
Abū Yūsuf’s return to this transmitted practice was akin to his return to many ḥadīths which he and his colleague Muḥammad later followed, abandoning their teacher’s opinion once they realized that their teacher himself held that such ḥadīths were proof if authentic, though they had not come to his attention. Anyone who imagines that Abū Ḥanīfah or any of the Imams of the Muslims would knowingly oppose an authentic ḥadīth because of analogy or anything else is mistaken; he speaks either from conjecture or from desire…
He then said: The point here is that the practice of the people of Medina which functions as a transmitted report is, by unanimous agreement of the Muslims, a binding proof. Mālik said as much to Abū Yūsuf when the latter asked him about the ṣāʿ and the mudd. Mālik ordered the people of Medina to bring their measures; they told him the chain of transmission went back to their forefathers. Mālik asked, “Do you think, Abū Yūsuf, that these people are lying?” He replied, “By Allah, they are not lying. I have examined these measures and found them to be five and one-third ratls according to your Iraqi weights.” Abū Yūsuf then said, “I revert to your view, Abū ʿAbd Allāh. Had my teacher seen what I have seen, he would have retracted just as I have.”
He questioned Mālik about the charity on vegetables. Mālik said, “Here are the vegetable markets of Medina; no charity was taken from them in the time of the Messenger of Allah ﷺ, nor in the time of Abū Bakr or ʿUmar (may Allah be pleased with them),” meaning that vegetables already grew there then. He asked him about endowments (aḥbās); Mālik pointed to various properties and said, “This is the endowment of so-and-so, and that is the endowment of so-and-so,” naming Companions for clarification. In each case Abū Yūsuf said, “I have returned, Abū ʿAbd Allāh. Had my teacher seen what I have seen, he would have retracted just as I have…”
This, then, is the first level of the consensus of the people of Medina, and it is binding proof by agreement of the Muslims. He then said: “The second level is the early practice of Medina before the martyrdom of ʿUthmān ibn ʿAffān.”