The ruling on a follower who leaves a pillar or an obligatory act in the prayer

Question : May Allah reward you. He says: If a follower leaves a pillar or leaves an obligatory act while he is following his imam in the prayer, what is required of him?

Answer : Yes. As for leaving an obligatory act, if it was intentional, his prayer is invalid. If it was due to forgetfulness, it is obligatory for him to perform the prostration for forgetfulness. Then, if he did not miss any part of the prayer, he says the closing salam with his imam, and the imam bears the prostration for forgetfulness on his behalf. Is that clear? If one leaves an obligatory act, what do we say? Say it. If it was intentional, the prayer is invalid. If it was due to forgetfulness, he says the salam with his imam. Why? Because the imam bears it on his behalf. Good. And if he was a follower and missed some of the prayer, and left an obligatory act due to forgetfulness, he prostrates for forgetfulness when he finishes his prayer before the salam. For example, if he missed a rak'ah: a person joined the imam in the second rak'ah of the Zuhr prayer, and he forgot to say "Subhan Rabbi al-A'la" in the prostration in one of the rak'ahs. This is leaving an obligatory act. How much did he miss? What did he miss? Think, my brothers. How much did he miss? Allah is the helper. How much did he miss in the example we gave, my brothers? He joined the imam in the second rak'ah of the Zuhr prayer. How much did he miss? Are you sure? Keep your composure, my brothers. Good. If he missed a rak'ah, he performs the rak'ah. When does he prostrate for forgetfulness? Before the salam. If he performs the rak'ah and recites the final tashahhud, he prostrates two prostrations for forgetfulness. This is if what was left was an obligatory act. But if what was left was a pillar, if it was intentional, the prayer is invalid. If it was due to forgetfulness, he performs a rak'ah in place of the rak'ah in which he left the pillar. He performs a rak'ah after the imam's salam. He performs a rak'ah after the imam's salam. An example of this is a man who joined the imam in the first rak'ah of the Zuhr prayer. In one of the rak'ahs, he did not prostrate except once; he forgot. The imam prostrated the two prostrations and stood up, but he prostrated the first prostration. Either he did not hear the imam, or for some reason he did not rise from the prostration. When the imam rose from the second prostration, he rose from the first prostration. So, two pillars remained for him: the sitting between the two prostrations, and the second prostration. We say this man cancels the rak'ah in which he left the pillar, and he performs a rak'ah after the imam, and he prostrates for forgetfulness after the salam, because he added something to his prayer due to forgetfulness. The prostration for forgetfulness, if it is due to an addition, is after the salam. If it is due to a deficiency, it is before the salam.