Sunan Abi Dawud 211
سنن أبي داود#211SahihNarrated 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiIsnaad Hasan
In-book reference: 1:211