What is the ruling on the prayer of the congregants and those who joined late if the Imam forgot the second prostration of the last rak'ah and concluded the prayer without performing it or the prostration of forgetfulness, and did not return to it after the people reminded him?

The situation of an Imam who, after the salām, was alerted by the congregants that he had missed a prostration, falls into one of two cases:

First: He is certain of his correctness and did not forget the prostration; in this case, his prayer is valid.

Second: He is not certain of his correctness; in this case, his prayer becomes invalid if he does not perform the prostration he forgot. The Imam must defer to the statement of the congregants who alerted him if they are two or more, even if he strongly believes himself to be correct. If he insists and is not certain of his correctness, his prayer becomes invalid.

Whoever followed the Imam in omitting the prostration, their prayer is invalid, whether they left the mosque or remained in it, and they must repeat it. They are not excused by their ignorance if learning was possible for them. As for the latecomer who caught the final tashahhud, their prayer is not invalidated by the invalidation of the Imam's prayer.