Is it true that Omar ibn al-Khattab led the people in prayer while he was in a state of ritual impurity (junub), and is it permissible for a person in a state of ritual impurity (junub) to lead the prayer?

Umar ibn al-Khaṭṭāb, may Allah be pleased with him, went out to his land and found traces of a wet dream. So he performed ghusl (definition) and washed away the traces, then prayed after sunrise. In another narration, he led the people in the Fajr prayer. It is not permissible for a Muslim to pray alone or with people while in a state of janābah if he is aware of his janābah and is able to remove it. However, if he is unable to do so due to the absence of water, or the inability to use it, or his unawareness of the wet dream, then there is no impediment to prayer at that time, and those who prayed behind him are not required to repeat their prayer.