Maliks Muwatta Book 2, Hadith Number 59.
Section : Indulgence in Not Having to do Wudu for Prostatic Fluid.
Yahya related to me from Malik that as-Salt ibn Zuyayd said, “I asked Sulayman ibn Yasar about a liquid I discovered. He said, ‘Wash what is under your garments with water and forget about it.'”