has not yet ended his prayer. But if the imam’s prostration is after the salam, must the follower follow him, or is he not required to do so?

The apparent meaning of the author’s words is that he must follow him even after the salam, due to the general implication of his statement, “except in following his imam.” Thus, there is no difference between the imam’s prostrating before or after the salam. This is clear when the follower has not missed any part of the prayer: in that case, he must prostrate with the imam, even after the salam.

But if the follower is making up missed rak‘ahs and the imam prostrates after the salam, must the follower join him in this prostration?

The apparent meaning of the author’s words is that he must do so, based on his statement, “except in following his imam.” This is the well-known view among the jurists; they even said that if he rises but has not yet fully stood upright, he must return, just as if he had risen after the first tashahhud (1).

The correct view in this matter is that, if the imam prostrates after the salam, the follower is not required to follow him, because following him at that point is impossible: the imam will say the salam, and if the follower were to join him in saying the salam, his prayer would be invalid, since the salam constitutes a separation preventing this (2).

But after he has completed his prayer, must he prostrate after the salam, just as the imam did?

The answer is that the matter requires further detail:

If the imam’s forgetfulness occurred in the portion of the prayer that the follower caught with him, then he must prostrate after the salam.