to those compilations, not everything written in the books is known to a single scholar, and it is scarcely possible for anyone to master them all. A person may own numerous volumes and still not grasp everything they contain.

Indeed, those who lived before these collections were compiled were far more versed in the Sunnah than later scholars, for much of what reached them with sound authority now comes down to us only through an unknown narrator, or with a broken chain, or does not reach us at all. Their ledgers were their own memories, which preserved many times what is found in the written compilations. Anyone familiar with the matter has no doubt about this.

Therefore, let no one claim, “Whoever is not acquainted with every single hadith cannot be a mujtahid.” If it were required of a mujtahid to know everything the Prophet ﷺ said and did that pertains to legal rulings, then, on that definition, there would be no mujtahid in the entire ummah. The most a scholar can attain is to know the majority, the greater part of that material, so that only a small amount of detail escapes him—yet it may happen that he disagrees with precisely that small portion which has reached him.

Second reason: a hadith may have reached the scholar but has not been established as sound in his view, either because its narrator, or the narrator’s teacher, or another transmitter in the chain is, in his judgment, unknown, suspected, or weak in retention.