The imam bowed before completing al-Fatihah, then performed a fifth rak'ah and prostrated for forgetfulness!!

Question:
He says: Honorable Shaykh, may Allah grant you success, a man led a congregation in the midday prayer. When he stood for the third rak'ah, a man entered and disturbed them, so he bowed before completing the recitation of al-Fatihah. Then he remembered afterward and performed a fifth rak'ah in place of the third, and prostrated for forgetfulness before the closing salam. Is his action valid? And what is required of the followers behind him when they followed him in the fifth rak'ah?

Answer:
Yes, if the imam did not complete al-Fatihah and bowed before completing it, he has left a pillar. And whoever leaves a pillar is like whoever leaves a complete rak'ah. So if he stands and performs a valid rak'ah in place of the rak'ah in which he left al-Fatihah, there is no harm. This is what is obligatory for him, and the followers follow him; the followers are followers of their imam. Yes.