Should a congregant who did not rise with the Imam for the fifth rak'ah out of forgetfulness, and waited until the Imam said the tasleem, perform the prostration of forgetfulness (sujood al-sahw) with him?

If the Imam stands for a fifth rak'ah out of forgetfulness, the congregants must alert him. If he does not return, the congregant should sit and recite the tashahhud. He may then either make the taslim and leave the Imam, or wait for him to make the taslim together.

Scholars are unanimous on the obligation for the congregant who caught the first rak'ah with the Imam to follow him in the prostrations of forgetfulness (sujud al-sahw), whether the Imam prostrates before or after the taslim, and whether he forgot alone or the congregant forgot with him. This is based on the Prophet, peace and blessings be upon him, who said: "Indeed, the Imam was appointed to be followed, so do not differ from him... and when he prostrates, then prostrate."