Is it permissible to expose the person who commits religious innovation, or to speak about him and criticize him?

The questioner : Is it permissible to expose the person who commits religious innovation, or to speak about him and criticize him?

The Shaykh : The person who commits religious innovation is in one of two states: either he keeps it to himself, or he is well-known among the people. In the first case, there is no need to expose him, because his harm is limited to himself. In the second case, it is necessary to expose him and warn people against him, so that the people who live among them are not deceived by him. This is not backbiting in any way, as some of the overly strict may imagine. The hadith: is a general statement with a specific exception. I have mentioned to you the words of some jurists in two lines of poetry in which they gathered the backbiting that is exempted from prohibition. One of them said:
"Censure is not backbiting in six cases: *** the complainant, the identifier, and the one who warns,
the one who openly commits open sinfulness, the one who seeks a ruling, *** and the one who seeks assistance in removing what is wrong."
Thus, describing the innovator and exposing him falls under identifying him and warning against him. Therefore, the scholars of hadith—may Allah reward them with good—agreed on describing many of the narrators of hadith with what they were upon of religious innovation. This is all part of their fulfillment of the obligation to clarify things for the people, so that they may know the righteous narrator and take from his creed, and the innovator narrator and leave him and his creed that deviates from the Book and the Sunnah.