If the ma'mum forgets the salutation upon the Prophet (peace and blessings be upon him) and says the taslim with the imam, is anything required of him?

Question : So, he sat with the ma'mum and the imam in the final tashahhud, and the ma'mum forgot the salutation upon the Prophet (peace and blessings be upon him), and the imam said the taslim, and he said it with him. Is it obligatory for him?

Answer : If we say that the salutation upon the Prophet (peace and blessings be upon him) is a pillar, then he must return to his prayer, recite the salutation upon the Prophet (peace and blessings be upon him), then say the taslim, and perform the prostration for forgetfulness after the taslim. If we say it is a sunnah (recommended practice) and not a pillar, then there is no need to return. If we say it is obligatory, then there is no need to return, but he must perform the prostration for forgetfulness for leaving an obligatory act. That is complete. If he prostrates, good. If he prostrates, I want [him to do so].