If the imam makes a mistake and adds a rak'ah to the prayer, and some people follow him while others do not, what is the ruling on that?

Question : If the imam makes a mistake and adds a rak'ah to the prayer, for example standing up for the fifth when it is the fourth, and some people follow him while others do not, what is the ruling on that? May Allah reward you with good.

Answer : The correct position is with those who did not follow him. If the imam stands up for the fifth and you are certain that it is the fifth, then recite the tasbih (subhan Allah) and he must return, even if he has already recited, even if he is in ruku' (bowing), he must return. If he does not return, you do not stand up with him; sit down and wait for him, and perform the taslim (closing salam) with him. As for the one who followed him in the extra rak'ah, if he did not know and thought that this was what was obligatory upon him, then he owes nothing. But if he knew that it was forbidden for him, then it is obligatory for him to repeat the prayer because he added a rak'ah to it knowing that it was extra and that following the imam in that is forbidden. May Allah reward you with good.