Musannaf Ibn Abi Shayba 1:1443

Muhammad ibn Fudayl narrated to us, from al-A’mash, from ‘Amr ibn Murrah, from Yusuf ibn Mahak, who said: A guest stayed with us and had a wet dream, and he had a wound. We came to ‘Ubayd ibn ‘Umayr and mentioned that to him. He said: "He should wash what is around it, and water should not touch it."