If the imam leads the congregation in prayer and then it becomes clear that he was not in a state of ritual purity, must the congregation repeat the prayer or not?

The questioner : The second question says: We prayed in congregation, and one of us led us in prayer. When the prayer was finished, he informed us that he had prayed without performing the ablution for prayer, having forgotten. Is it obligatory for us to repeat the prayer?

The Shaykh : It is not obligatory for you to repeat the prayer, because your prayer is valid. As for him, it is obligatory for him to repeat the prayer, because his prayer is not valid. Likewise, if he realizes during the prayer that he is not in a state of ritual purity, or if he remembers during the prayer that he is not in a state of ritual purity, he should leave and instruct one of you to complete the prayer for you, and you should build upon what has passed of your prayer. This is because there was nothing in your prayer that invalidates it, and you entered into it with the permission of the Lawgiver, and you followed this man with the permission of the Lawgiver. What follows from what is permitted is in accordance with the truth. Some scholars held the view that if the imam realizes during the prayer that he is in a state of minor or major ritual impurity, his prayer and the prayer of those behind him are invalid. However, this opinion is weak, because there is no evidence for the invalidity of the prayer of those behind him. And if there is no evidence, then their prayer, which they entered into based on a legal proof, cannot be invalidated except by a legal proof.

The questioner : Yes, the third question says.