If the imam forgets in the last rak'ah and does not perform the last prostration, then he says the taslim and the ma'mums leave, some of whom perform the prostration alone and some of whom repeat the prayer

The questioner : O Shaykh, I prayed in congregation and they prayed one of the obligatory prayers, and the imam forgot the last prostration in the last rak'ah and did not prostrate, but said the taslim and the ma'mums left. Some of the ma'mums performed the prostration, separating from the imam, some of them went out of the mosque, and some of them repeated the prayer entirely. Then the imam remembered, so he left and stood up for the prostration and said the taslim, but he did not perform the prostration for forgetfulness. It is known that prostration is a pillar and the prayer is invalid whether the omission was due to forgetfulness or intentionally, so what is the ruling?

The Shaykh : But he performed the prostration, he just did not perform the prostration for forgetfulness?

The questioner : The prostration only.

The Shaykh : And he did not perform the prostration for forgetfulness.

The questioner : Yes, what is the ruling for the ma'mums?

The Shaykh : It is obligatory for the ma'mum, if his imam neglects a pillar or an obligatory act, to alert him. The Prophet (peace and blessings be upon him) said: So it is obligatory for the ma'mums to glorify Allah and to persist in glorifying Allah until the imam returns. If it happens that the imam does not understand, let them recite a verse that points to it. For example, this man who left the last prostration and said the taslim, it is obligatory for the ma'mums to glorify Allah and say Subhan Allah until he notices. If he does not notice, let them recite a verse from the Qur'an that reminds him, such as saying: or a verse like it that reminds him. As for the case that occurred, those who performed the second prostration and said the taslim, their prayer is valid. Those who did not prostrate until a long time had passed, it is obligatory for them to repeat the prayer from the beginning. Those who remembered shortly after and then prostrated, it is obligatory for them, after the taslim, to prostrate two prostrations for forgetfulness and then say the taslim. So you ask these brothers who did what they did. Whoever among them says that he has not prostrated until now, I order him to repeat his prayer from the beginning. Yes.