Musannaf Ibn Abi Shayba 1:970

Abu Mu'awiyah narrated to us, from al-A'mash, from Sulayman ibn Mushir, from Kharasha ibn al-Hurr, who said: 'Uthman was asked about prostatic fluid (madhy), and he said: "That is the dripping, and from it is the ablution (wudu)."