Criticism of Hadith thus provides "certainty of knowledge" of what Muhammad said, in fact it is only the much rarer subset of sahih -- "mutawatir" hadith -- that provide certain knowledge. "Mutawatir" means the report "of a large number of narrators whose agreement upon a lie is inconceivable. This condition must be met in the entire chain from the origin of the report to the very end." However, according to Wael Hallaq, "the bulk of hadith with which the traditionists dealt, and on the basis of which the Jurists derived the law" were known as "ahad" — i.e. non-"mutawatir" hadith; Hadith without "textually
Hadith of the Ark follows: Behold! The similitude of my Ahlul Bayt, is like that of the Ark of Noah: The one who embarks it, will have saved himself, and the one who turns away from it, is doomed. Many Sunni books narrate this Hadith. Some significant Sunni books that narrate this Hadith are: Al-Hakim al-Nisaburi, one of the greatest Sunni scholars, narrated this hadith as authentic (sahih) in his Mustadrak. Al-Heithami in his book ("written against Shia") states: By many narrations of this hadith which strengthen each other;""certainly Ahl al-Bayt are like the Ark of Noah, saved Whoever boarded"", and in Sahih Muslim