Musnad Ahmad 5:261

'Abdullah narrated to us, Ahmad ibn 'Isa narrated to me, 'Abdullah ibn Wahb narrated to us, Makhramah ibn Bukayr informed me, from his father, from Sulayman ibn Yasar, from Ibn 'Abbas, who said: 'Ali ibn Abi Talib said: We sent al-Miqdad ibn al-Aswad to the Messenger of Allah, may Allah bless him and grant him peace, and he asked him about the *madhy* (pre-seminal fluid) that comes out of a person: "What should he do?" The Messenger of Allah, may Allah bless him and grant him peace, said: "Perform ablution (*wudu*), and sprinkle your private part with water."