Musannaf Ibn Abi Shayba 1:984

Waki’ narrated to us, he said: Sufyan narrated to us, from Mansur, from Mujahid, from Ibn Abbas, he said: Regarding semen, prostatic fluid (madhy), and urethral discharge (wady): As for semen, in it is the ritual bath (ghusl). As for prostatic fluid and urethral discharge, in them is ablution (wudu), and he should wash his private part.