Sunan An-Nasai, Chapter: The Book of Purification

that Ali told him to ask the Messenger of Allah (saw) about a man who comes close to his wife and prostatic fluid comes out of him - what should he do? (Ali said:) For his daughter is married to me and I feel too shy to ask him. So I asked the Messenger of Allah (saw) about that and he said: "If any one of you experiences that, let him sprinkle water on his private part and perform Wudu as for Salah." (Sahih)