Tafsir of Sad 38:7

"We have not heard of this"—that which he says—"in the latest religion." Ibn Abbas, Mujahid, Muhammad ibn Ka'b, and Muqatil held that they meant the religion of the Christians, and the description of it as "the latest" refers to [their] belief, because they are the ones who do not believe in the prophethood of Muhammad, may Allah exalt him and grant him peace. Their intent by saying "We have not heard of this," etc., is that we have heard the opposite of it, which is [the rejection of] monotheism; for the Christians practiced trinitarianism and claimed it was the religion brought by Isa, upon him be peace—and far be it from him to have done so.

It is also narrated from Mujahid and Qatadah that they meant the religion of the Arabs and the sect upon which they found their forefathers. It is also permissible that "in the latest religion" acts as a circumstantial qualifier (hal) for the demonstrative pronoun ("this"), not as a prepositional phrase attached to "heard." That is: "We have not heard of this which he calls us to—[namely] monotheism—as existing in the religion that would be at the end of time." They meant that they had not heard from the People of the Scripture or the soothsayers—who used to inform them before the mission of the Prophet, may Allah exalt him and grant him peace, of the appearance of a prophet—that his religion would contain monotheism.

They lied in that assertion, for the report that the Prophet sent at the end of time would break the idols and call to the monotheism of the All-Knowing King was the most famous of matters before his emergence. If they meant by this interpretation that they had heard the opposite of this, then their falsehood is all the more heinous.

That is, an invention and a slander without any precedent for it.