What is the ruling regarding someone who led people in prayer, believing himself to be in a state of ritual purity, then discovered after the prayer the presence of traces of a wet dream on his clothes?

If the Imam leads the people in prayer and then finds semen on his garment, and no one else sleeps in that garment, then he must perform ghusl (definition) (ritual bath) and repeat the prayers he performed after his last sleep, because they were invalid. As for the prayers of the congregants (ma'mumeen), they are valid, according to the more preponderant opinion, because they are excused as they were unaware of their Imam's state of ritual impurity. Ibn Qudamah is of the view that the Imam's prayer is invalid in this case, while the congregants' prayer is valid. This has been narrated from Umar, Uthman, Ali, and Ibn Umar, may Allah be pleased with them, and it is the opinion of Malik and Al-Shafi'i. As for semen, there is a difference of opinion regarding its impurity, and the more preponderant opinion is that it is pure.