If the imam innovates in the prayer, is it prescribed for him to appoint a substitute?

Question:
He says: Honorable Shaykh, may Allah grant you success, if the imam innovates while he is sitting, does he wait until he stands up and appoints a substitute, or does he hasten to appoint a substitute? And how is that done? If he innovates before appointing a substitute, according to the school of thought, the prayer is invalid.

Answer:
Regarding appointing a substitute: if he senses that his ablution is about to be broken, he appoints a substitute. But if his ablution is broken before he appoints a substitute, I say his prayer is invalid, so there is no appointing a substitute.