The ruling on the prayer of one who raises his head from prostration before the imam due to a mistake

Question:
He says: Honorable Shaykh, may Allah grant you success. A man prayed behind an imam with a weak voice, so he raised his head from prostration before the imam, thinking the imam had already raised his head. He did not go back and completed his prayer in this state. He asks about the ruling on this prayer of his, and whether he has to repeat what he prayed after it if he is required to repeat it?

Answer:
As long as he raised his head before the imam while excused, being ignorant of it, he owes nothing; because the prostration took place, he prostrated, but he raised his head from it before the imam due to a mistake, not intentionally. His prayer is valid, if Allah wills.