A latecomer discovers that the imam prayed five rak'ahs: what should he do?

Q: If a latecomer joins the imam and prays two rak'ahs with him, and then it becomes clear to him that the imam has prayed five rak'ahs, does he count the extra rak'ah he prayed with the imam, such that he only performs two rak'ahs, or does he not count it and perform three?

A: The correct view is that he does not count it, because it is invalid in the legal ruling, and it is obligatory not to follow the imam in it for one who knows that it is extra. The latecomer should not count it, and this questioner must make up three rak'ahs, because in reality he only caught one rak'ah. And success is from Allah.