(83) باب فِي الْمَذْىِ
Narrated Abdullah ibn Sa'd al-Ansari:
I asked the Messenger of Allah (ﷺ) as to what makes it necessary to take a bath and about the (prostatic) fluid that flows after taking a bath. He replied: that is called madhi (prostatic fluid). It flows from every male. You should wash your private parts and testicles because of it and perform ablution as you do for prayer.
Reference: Sunan Abi Dawud 211
In-book reference: Book 1, Hadith 211
English translation: Book 1, Hadith 211