The ruling on one who forgets in the Tarawih prayer and adds a rak'ah

The questioner : In the name of Allah, the Most Gracious, the Most Merciful. All praise is due to Allah, Lord of the worlds, and may peace and blessings be upon the noblest of the prophets and messengers, our Prophet Muhammad, and upon his family and all his Companions. As for the ruling, due to the frequent occurrence of this among people, and knowing that it is not specific to me, I have learned from your eminence some of its rulings, and I hope you will not excuse me for this, given the widespread need for it. He mentions the points, saying: The first point is: If one forgets while praying in the Tarawih prayer and adds a third rak'ah, and does not remember until he is at the end of the third, or at the beginning of the fourth, what should he do?

The Shaykh : And the thing, may Allah know, and what is it.

The questioner : And he says, may Allah know, that it is not specifically for me, but for the general benefit of my brothers.

The Shaykh : All right, if Allah wills. In the name of Allah, the Most Gracious, the Most Merciful. The Tarawih prayer is part of the night prayer. The Prophet (peace and blessings be upon him) said: He stood in Tarawih until the third, then remembered. It is obligatory for him to return. If he does not do so, his prayer is invalid, based on the saying of the Messenger of Allah (peace and blessings be upon him): If he remains in a state of forgetfulness until he sits for the tashahhud, then he only has to perform the prostration for forgetfulness after the taslim. Why after the taslim? Because it is an addition, and every forgetfulness regarding an addition is done after the taslim. Yes.

The questioner : He says: If he is at the beginning of the fourth, what does he do? Hmm.

The Shaykh : If