Maliks Muwatta Book 2, Hadith Number 57.
Section : Wudu on Account of Prostatic Fluid.
Yahya related to me from Malik from Zayd ibn Aslam from his father that Jundub, the mawla of Abdullah ibn Ayyash, said, “I asked Abdullah ibn Umar about prostatic fluid and he said, ‘When you find it, wash your genitals and do wudu as for prayer.'”