The ruling on one who prays behind an imam whose ritual purity is not valid

Question:
The listener Sa'd Khumays al-Dawsari sent a message saying: If I pray behind an imam, and during the prayer I notice that there is a spot on one of his feet that the water did not reach, and I pointed it out to him after the prayer but he did not care, so I repeated the prayer, what is the ruling on what I did?

Answer:
If the imam prays with the people, and then it becomes apparent that he is in a state of ritual impurity, or that his ritual purity is not valid, then the prayer of the followers is valid. This is the correct position; their prayer is valid. It is he who must repeat it if he knows that he is in a state of ritual impurity or that there is a defect in his ritual purity that invalidates it. He must repeat it, not the congregation. Their prayer is valid, and it is obligatory for him to repeat it. Yes.

The presenter: May Allah reward you with good. And if the follower repeated the prayer believing that his action was correct?

The Shaykh: There is no blame on him. If he repeated it based on his own independent legal reasoning, there is no blame on him. But he should know the ruling of the Shari'ah, and that he does not have to repeat it. So if he repeats it thinking that he has to repeat it, he is rewarded, if Allah wills.

The presenter: May Allah reward you with good.