What is the ruling on the follower continuing to pray behind the Imam if the Imam forgets a prostration and does not return after being prompted by the follower, or if the Imam adds an extra rak'ah and does not return, with the follower not continuing with him in the extra rak'ah?

If the Imam forgets a prostration (sujud), the follower (ma'mum) should alert him. If the Imam does not perform it, the follower should perform it himself and intend to separate from the Imam, completing his prayer individually. The Imam is obligated to perform the prostration if two trustworthy individuals alert him, unless he is certain of his own correctness. If the prayer concludes and the followers alert him, he should perform one rak'ah. It is not permissible for the follower to follow the Imam in omitting a prostration, otherwise his prayer will be invalidated.

If the Imam adds an extra rak'ah and is alerted but does not return, the follower has the choice between separating from him and completing his prayer individually, or waiting for the Imam to conclude the prayer with him. If the Imam prostrates for forgetfulness (sujud as-sahw), the follower should prostrate with him, based on the general meaning of the Prophet's ﷺ saying: "Indeed, the Imam is appointed to be followed." Some scholars, however, are of the view that it is obligatory for the follower to separate from the Imam in this situation.