What about someone who joins the congregational prayer late and has to make up the rak’aat missed, and finds that the Imam makes sujood al-sahw? Should he join in the sujood or stand and continue his prayer and make it at the end?
If the Imam makes the salaam and the follower stands up to complete what he missed, while the Imam has to make prostrations of forgetfulness after the salaam, the follower should return back and make prostrations with the Imam if he has not completed standing upright. Otherwise he should not return. He should complete his prayer and after it he should make the missed prostrations. The evidence for this is the same as presented in the discussion for Forgetting to sit for tashahhud between the second and third raka’ah. (al-Mughni 1/697)