From Sahih Muslim (Hadith 697):
Ibn 'Abbas reported it from 'Ali:We sent al-Miqdad b. al-Aswad to the Messenger of Allah (ﷺ) to ask him what must be done about prostatic fluid which flows from (the private part of) a person. The Messenger of Allah (ﷺ) said: Perform ablution and wash your sexual organ
Reference: Muslim 697