Musnad Ahmad 1101:1

Yazid ibn Harun narrated to us, Muhammad ibn Ishaq informed us, from Hisham ibn Urwah, from his father, from al-Miqdad ibn al-Aswad, who said: Ali said to me: "Ask the Messenger of Allah, may Allah bless him and grant him peace, about a man who plays with his wife, and *madhy* (pre-seminal fluid) comes out of him without the water of life (semen). For were it not that his daughter is under my care, I would have asked him." So I said: "O Messenger of Allah, a man plays with his wife, and *madhy* comes out of him without the water of life?" He said: "He shall wash his private part and perform his ablution for prayer."