The ruling on following the imam when the ma'mum knows of an error in his prayer

Question:
Does faith remain if the five prayers or others are increased, or if there is a lapse in their conditions? And what should the teacher do if he is certain of an error in his faith? We seek detail on this issue, as the Messenger of Allah (peace and blessings be upon him) did.

Answer:
If one knows that the imam has omitted a standing, bowing, or prostration, he does not follow him, but waits for the imam to return. If the imam stands for the fifth rak'ah and the person knows it is the fifth, he does not stand with him; he sits. If he wishes, he says the taslim for himself; if he wishes, he waits until the imam says the taslim, then says the taslim for himself. If he wishes, he intends to separate from the imam, recites the tashahhud, and says the taslim for himself. If he wishes, he waits until the imam returns, recites the tashahhud, and says the taslim, so he says the taslim with him. The important point is that he does not follow him in what he believes is not permissible in the prayer, whether it be a rak'ah or a bowing. He waits for him to return, then follows him for the remainder.