What is the ruling on the prayer of someone who leaves the mosque after the imam's first salutation, and does the imam's prayer end with the first or second salutation after he forgets the middle sitting?

We clarified that whoever omits the first tashahhud, it is prescribed for him to prostrate before the taslim, even though his prostration after the taslim is permissible. And that the preponderant opinion is the dropping of the prostration of forgetfulness and the validity of the prayer if the interval is prolonged or if one exits the mosque. So if he made the taslim and remembered, he must prostrate if the time is near. However, if the interval is prolonged, or he breaks his wudu, or exits the mosque, he does not prostrate and his prayer is valid.

As for the ma'mum (follower), he must follow the imam in prostration. If he forgets to follow him, he should return to it if the interval is not prolonged; otherwise, he must repeat the prayer. It is more cautious to instruct these individuals to repeat their prayers in which they failed to follow the imam in the prostration of forgetfulness.

The imam's prayer ends with the first taslim. And whoever omits the obligatory prostration, the preferred place for which is after the taslim, commits a sin but his prayer is valid, because he has already exited the prayer, so it does not affect its invalidation.