What is the ruling on one who forgot a prostration in his prayer?

The questioner: What came regarding the last prostration; meaning, he prostrated one prostration and did not prostrate the other, so he naturally said the closing salam... that you did not prostrate; you did not complete the one prostration.

The Shaykh : Yes.

The questioner: So what is the solution, I mean?

The Shaykh: Yes, what did he do?

The questioner: He?

The Shaykh : Yes.

The questioner: I do not know, the report was passed to me today; meaning, he.

The Shaykh: He prostrates the prostration that he missed.

The questioner: Yes.

The Shaykh: Then he follows it with two prostrations, the prostrations for forgetfulness.

Another questioner: For forgetfulness.

The Shaykh: All right, one of our brothers asks here that an imam forgot a prostration from the two prostrations of a unit of prayer, so when he said the closing salam, he was reminded of the prostration he had forgotten, so I said to him: What did he do? He said: I do not know, this is how the news came to me, and what appears to me is that this one who forgot the prostration and was then reminded of it; the matter is easy for him, and that is by returning and prostrating the prostration that he missed from the body of the prayer, then following it with the two prostrations for forgetfulness, and thus all of this is derived from several incidents that occurred to the Prophet (peace and blessings be upon him), so when he was reminded, he performed what he had forgotten from the prayer, so in the incident of the man with the two hands, which the two Shaykhs narrate in their "Sahih"s from the hadith of Abu Hurayrah (may Allah be pleased with him), he said: While we were praying with the Prophet (peace and blessings be upon him), he prayed two units, then said the closing salam, then he moved to a side of the mosque, and there was a man known as the man with the two hands, so he said: O Messenger of Allah, did the prayer become short or did you forget? He (peace be upon him) said: = -- May Allah have mercy on you -- = He said: Yes, it did. So the Messenger of Allah (peace and blessings be upon him) looked at the Companions, and among them were Abu Bakr and 'Umar, and he said: . They said: Yes, O Messenger of Allah. So he came to the place of prayer where he had been praying, and I do not say he came to the prayer niche; because there was no prayer niche in the mosque of the Messenger. - This is for the one who walks! - .

The questioner : May Allah reward you with good.

The Shaykh: Yes, indeed, and he only came to his place of prayer, so he prayed two units, then said the closing salam to his right and to his left, he prostrated two prostrations, then said the closing salam to his right and to his left, and it did not become authentic on this occasion that he repeated the tashahhud, meaning the tashahhud of the prostrations for forgetfulness; because some schools of jurisprudence - such as the school of Abu Hanifah - say: After he prostrates the two prostrations for forgetfulness, he recites the tashahhud of the prayer, then says the closing salam, this is what is established in an authentic hadith, rather, in this hadith there is what indicates to us that after he prayed the two units, and prostrated the two prostrations for forgetfulness; he said the closing salam immediately, and did not recite the tashahhud a second time after the two prostrations.
In another incident, he (peace and blessings be upon him) prayed the sunset prayer two units, so even in this narration there is something extra compared to the hadith of Abu Hurayrah, in the hadith of Abu Hurayrah there is something I did not mention earlier for the sake of brevity; which is that when the Prophet (peace and blessings be upon him) said the closing salam from the two units, and moved to a side of the mosque; the people quickly went out, and most of the people knew that they were praying behind the Messenger, and the Messenger of Allah (peace and blessings be upon him) was connected to the revelation from the sky every hour, so perhaps it occurred to their minds and thoughts that the prayer had become short; and therefore they stopped, meaning they hardly believed the Messenger when he said: Peace be upon you, until they were about to leave, those who remained remained, and among them remained - as we mentioned earlier - the man with the two hands, and what we mentioned earlier took place.
The second story is that when the Messenger (peace be upon him) prayed the sunset prayer two units; - also - the people left, so it was said to him: You prayed two units, so he ordered here the iqamah for the prayer, and that is to gather the people, and the iqamah for the prayer was renewed and he prayed one unit, which is the missed unit, and he prostrated - also - the two prostrations for forgetfulness, then said the closing salam, so if a worshipper misses a pillar of the pillars of the prayer, it is sufficient for him to perform it, and to make up for it when he remembers, whether he was in the prayer, or he was reminded of it after the prayer, but he must prostrate the two prostrations for forgetfulness to compensate for this error that occurred from him in the prayer.