If the imam performs the prostrations of forgetfulness after the closing salam, is the prayer of the ma'mums who stood up and then returned to prostrate with the imam valid?

The questioner: Our Shaykh.

The Shaykh: Go ahead.

The questioner: That is, if there was an error by the imam, and the imam said the salam and then performed the prostrations of forgetfulness. The prostration of forgetfulness, of course, there was a masbuq, of course after the salam, meaning after he said the salam, he came and prostrated the two prostrations of forgetfulness, as is well known, before the salam and after the salam. There was a masbuq or several masbuqs, so when they saw the imam prostrating, they returned from standing and went down and prostrated. What is the ruling on their prayer in this case?

The Shaykh : It is valid.

The questioner: Now, is it said that they left a pillar for a recommended practice?

The Shaykh: Intentionally?

The questioner: But what is done with the ruling, Shaykh?

The Shaykh: Intentionally? The answer: No.

The questioner: Yes.

The Shaykh: Second, you say: a recommended practice. What recommended practice did you mean?

The questioner: The intended meaning is the obligatory.

The Shaykh: Is the prostration of forgetfulness a recommended practice? No, rather it is obligatory.

The questioner: Yes.

The Shaykh: So, first: he did not intend that return, but rather he intended to fulfill an obligation, which is his saying (peace and blessings be upon him): . So when the imam said the salam, he stood up, thinking that this was the salam of release, as is in the hadith. And when it became clear to him that it was not so, because he saw the imam prostrating, he followed him in that. So he did what was obligatory upon him, and it is not said that he left a pillar for a recommended practice! Rather, it is not said: he left a pillar for an obligation, because this is the obligation, so I see nothing at all in this issue.