It was narrated that 'Ali said:
"I was one who had a lot of prostatic discharge, so I asked the Prophet (ﷺ) and he said: 'If you see Madhi (prostatic fluid) then perform Wudu' and wash your penis, but if you see semen ejaculated, then perform Ghusl.'" (IT)
English reference (IT): Vol. 1, Book 1, Hadith 194 (IT)
Arabic reference (IT): Book 1, Hadith 195 (IT)