What is the ruling on the prayer of one who bows twice in a single rak'ah due to forgetfulness, and is a prostration of forgetfulness (sujud as-sahw) or a prostration of recitation (sujud at-tilawah) obligatory upon him in this case?

If the Imam prostrates for recitation and the worshipper does not know, so he bows, and then he realizes while the Imam is still prostrating, he must follow him and prostrate. If he does not realize until after the Imam has raised his head, then he stands up and follows the Imam for the remainder of his prayer, and he does not prostrate for recitation, because it is a sunnah and its time has passed.

If a worshipper prostrates for forgetfulness after the Imam has finished the prayer, and he does something that is not prescribed, his prayer is still valid because he was ignorant of the ruling. As for making up the prostration of recitation after the prayer, there is a difference of opinion among scholars, and the preponderant view is that it is not prescribed, because it is a sunnah and its time has passed.