The imam not responding to the congregation's tasbih when he makes a mistake

Question:
We prayed behind an imam who prayed the midday prayer in three rak'ahs. We reminded him by saying tasbih, but he did not stand up. Then he performed the prostration for forgetfulness. Some of the worshippers prostrated with him, while others did not; rather, they stood up, completed the fourth rak'ah, and said the closing salam.

Answer:
It is obligatory for the one who knows that the prayer is deficient to say tasbih and to point it out. If he stands up, that is fine; otherwise, they stand up and complete the prayer. As for him, he acts according to his independent legal reasoning. If he knows that he is correct, he sits and says the closing salam.
As for when he does not have control over the situation, he must yield to those who are saying tasbih and pointing it out to him. He should stand up and perform the fourth rak'ah. For this reason, when the Prophet (peace and blessings be upon him) was reminded in one of the two evening prayers that he had said the closing salam after two rak'ahs, he stood up when he was certain of their statement, and he completed the prayer. Similarly, in the second hadith, the hadith of 'Imran, when he was reminded that he had prayed three rak'ahs, he stood up and performed the fourth rak'ah—(peace and blessings be upon him).
Therefore, it is obligatory for the imam to yield to the congregation when they say tasbih for him and to act on their pointing out. If he was deficient, he completes it; and if he was excessive, he goes back. Except if he knows that he is correct, that he is certain of this, and that they are mistaken; then he acts according to his certainty.