What is the ruling if the imam forgets, says the closing salam, and does not perform the prostration for forgetfulness?

Question:
The imam prayed and made a mistake in the prayer, but he did not perform the prostration for forgetfulness, and the people left the prayer. What is the ruling? May Allah reward you with good.

Answer:
It is obligatory for him... he was commanded to prostrate; it is obligatory for him to perform the prostration for forgetfulness. If he left it off out of forgetfulness or ignorance, he owes nothing... but it is obligatory for him to prostrate, and it is obligatory for the followers to alert him: "Glory be to Allah." When he says the closing salam, they say the closing salam and alert him with words: "Did you not prostrate? You have a mistake, so prostrate." They alert him, just as the Companions alerted the Prophet (peace and blessings be upon him) when he said the closing salam after two rak'ahs, and when he said the closing salam after three, and when he added a fifth, they alerted him with words, (peace and blessings be upon him).
So if he makes a mistake by adding a rak'ah and says the closing salam and sits, they alert him, even with words. They say the closing salam and alert him. If "Glory be to Allah" is sufficient, they say it: "Glory be to Allah" before he says the closing salam. And when he says the closing salam, they say the closing salam and alert him with words. And if he left it off out of ignorance or forgetfulness, the prayer is valid.