Musannaf Ibn Abi Shayba 3:1595

'Abdah narrated to us, from Yahya bin Sa'id, from Sulayman bin Yasar, that 'Umar performed the morning prayer, then he went early to a land of his in al-Jurf. He found traces of a wet dream on his garment. He said: So he washed the [traces of the] wet dream and performed ghusl (ritual bath), then he repeated the morning prayer.