An imam who innovated in his prayer and completed it, and a long time has passed

Question:
Honorable Shaykh, may Allah grant you success. An imam prayed with the people, then he innovated in his prayer during the prayer and completed it without breaking it, and a long time has passed. What is required of him now?

Answer:
His prayer is invalid, and the prayer of those behind him is valid, if Allah wills, as long as they did not know. However, if they were aware, their prayer is invalid. But they would not be aware, and he did not inform them, so their prayer is valid. As for him, he must repeat the prayer. Even if a hundred years have passed, it remains a debt on him, and he must make it up. Yes.