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.'" (JA)
English reference (JA): Vol. 1, Book 1, Hadith 193 (JA)
Arabic reference (JA): Book 1, Hadith 194 (JA)