What does the ma'mum do if the imam adds a fifth rak'ah?

Question:
He says: Honorable Shaykh, may Allah grant you success, what does the ma'mum do if the imam adds a fifth rak'ah? Does he sit and wait until the imam says the taslim, and then say the taslim with him?

Answer:
It is obligatory for him to indicate this by saying Subhan Allah. It is obligatory for him to alert the imam. If the imam does not return, and the ma'mum believes that the extra rak'ah is not part of the prayer, he should sit. If he wishes, he may say the taslim for himself, or if he wishes, he may wait and say the taslim with him. Yes.