The obligation of one who forgets a prostration in his prayer

A message has reached the program from our brother Ali ibn Sulayman from Makkah al-Mukarramah. We presented some of his questions in a previous episode, and in this episode he asks and says: If a person prays the four-rak'ah prayer and does not prostrate in one of its rak'ahs except for one prostration, is the prostration for forgetfulness sufficient for him, or should he perform an additional rak'ah and then prostrate for forgetfulness afterwards?
Answer: If a worshipper omits a prostration due to forgetfulness, he should perform it immediately. If he does not remember until after he has stood up and begun the recitation, he should complete his prayer and perform an additional rak'ah, adding a complete rak'ah in place of the rak'ah in which he left the prostration, then prostrate for forgetfulness before saying the closing salam, and then say the salam. As for if he remembers immediately when he raises his head from the prostration, he should prostrate, return and prostrate the second time, and then prostrate for forgetfulness if he has already stood up. But if he is before standing up for the second prostration, he prostrates the second time and there is no prostration for forgetfulness required of him. Yes.
The presenter: If he prostrates for forgetfulness and then sits for the salam, but he recites the tashahhud, and perhaps he reaches the middle of it or finishes it, what should he do? Should he prostrate for forgetfulness for that, or should he say the salam?
The Shaykh: If he recites the tashahhud after his prostration for forgetfulness, it does not harm him. It does not harm. Yes.