It was narrated that 'Ali said:
"I was one who had a lot of prostatic discharge, and the Messenger of Allah (ﷺ) said to me: 'If you see Madhi (prostatic fluid) then wash your penis and perform Wudu' like that for Salah, but if you ejaculate semen, then perform Ghusl.'" (ES)
English reference (ES): Vol. 1, Book 1, Hadith 193 (ES)
Arabic reference (ES): Book 1, Hadith 194 (ES)