he records it as consensus.

The evidential basis of consensus
The majority of legal theorists hold that consensus is not an independent source in and of itself; rather, it must rest upon evidence drawn from the Quran or the Sunnah, whether or not we actually know that evidence, for it is sufficient that the consensus has reached us through sound transmission.

They say this because, if consensus were an autonomous source, it would amount to establishing new legislation after the Prophet ﷺ—and that is impermissible.

The same majority also maintain that one consensus cannot abrogate another. If the first consensus were definitive, and we were to suppose the second definitive as well, the matter would be impossible: the community has already united on the first, and the community does not unite upon error. Hence the later consensus would be deemed mistaken, for it contradicts a conclusive proof; it is inconceivable that a subsequent definitive consensus could abrogate an earlier definitive consensus.

Analogy (qiyās)
Meaning: extending a ruling from an original case to a subsidiary case because the two share the same effective cause.

Every valid analogy requires four elements:

1. The case to which comparison is made, called the original (asl);
2. The case being compared, called the subsidiary (farʿ);
3. The shared attribute that links the original and the subsidiary, called the effective cause (ʿillah);
4. The legal ruling transferred from the original to the subsidiary.