Sahih Muslim Book 3, Hadith Number 595.

Chapter : On al-Madhi.

Ibn ‘Abbas reported it from ‘Ali: We sent al-Miqdad b. al-Aswad to the Messenger of Allah (may peace be upon him) to ask him what must be done about prostatic fluid which flows from (the private part of) a person. The Messenger of Allah (may peace be upon him) said: Perform ablution and wash your sexual organ.