If the worshiper does not remember whether he performed one of the Sunan (plural of Sunnah, referring to recommended practices) in his prayer, should he perform the prostration of forgetfulness (sujud al-sahw) after the Imam's salutation, or should he give the salutation with him?

The prostration of forgetfulness (Sujud Al-Sahw) is waived for the congregant (ma'mum) if he forgets while following the Imam, because the Imam bears that on his behalf. However, if he is a latecomer (masbuq) and forgets after he has left the Imam, then he must perform the prostration of forgetfulness, and his ruling in this regard is the same as that of a person praying alone.