behind him in that case as well, and not abandon the congregation. If he abandons it, he is sinning and acting contrary to the Book, the Sunnah, and the practice of the early generations.

He was asked:

A man led the prayer without ablution, unaware of this, or had an impurity on him of which he was unaware. Is his prayer valid or not? If his prayer is valid, is the prayer of those following him also valid? Please give us a ruling, and may you be rewarded.

He replied:

If someone praying behind an imam does not learn of the imam’s state of ritual impurity, or of the impurity on him, until the prayer has ended, he does not have to repeat the prayer according to al-Shāfiʿī. The same applies according to Mālik and Ahmad if the imam himself was unaware. The imam alone must repeat the prayer if he was in a state of ritual impurity.

This was the established practice of the Rightly Guided Caliphs: they led the people in prayer, then discovered afterward that they had been in a state of major ritual impurity. They repeated their prayers but did not instruct the people to repeat theirs. And Allah knows best.