Musnad Ahmad 5:413

Narrated to us Abdullah, narrated to me Shayban Abu Muhammad, narrated to us Abd al-Aziz ibn Muslim—meaning Abu Zayd al-Qasmali—narrated to us Yazid ibn Abi Ziyad, from Abd al-Rahman ibn Abi Layla, from Ali, who said: I was a man who frequently produced prostatic fluid (madhy), so I asked the Messenger of Allah, peace and blessings of Allah be upon him, about that. He said: "For prostatic fluid (madhy), there is ablution (wudu), and for seminal fluid (maniy), there is a full ritual bath (ghusl)."