The indicators that reveal whether a narrator is telling the truth or lying are many and varied, and this is not the place to set them out in full. What matters here is that the Muslims have received—by uninterrupted, mass transmission—the very wording of the Qur’an and the unanimously agreed meanings it conveys, together with the mass-transmitted Sunnah. They also possess from their Prophet numerous other reports whose truth is known through multiple avenues: the endorsement of the error-protected community, the testimony of ordinary experience, and similar proofs. They carry the Qur’an in their hearts and do not depend on a written codex for its preservation; were every written muṣḥaf to vanish from the face of the earth, that would not diminish what they have memorised.
By contrast, if the People of the Book were to lose every copy of their scriptures, they would have no mass transmission of the actual wording. At best a handful among them may have memorised parts of it, yet their precision cannot be trusted. For this reason, once prophecy was cut off from them, alteration entered their books: sometimes by changing certain rulings and meanings, at other times by changing parts of the wording without anyone correcting it.
Thus they possess nothing akin to the Muslim system of isnād (chains of transmission), nor do they engage—as Muslims do—in scrutinising transmitters, declaring some reliable, criticising others, and researching the states of those who convey knowledge. There is neither textual nor rational proof that they are protected from unanimous error; on the contrary, it is known that they did in fact unite upon error when they denied the Messiah, and later when they denied Muhammad—may Allah bless him and grant him peace.
Accordingly, if the books transmitted from the earlier prophets are of the same category as those transmitted from Muhammad, yet are not mass-transmitted from them, and if the endorsement of anyone not protected from error carries no authoritative weight, then they are left without