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.'" (ES)
English reference (ES): Vol. 1, Book 1, Hadith 194 (ES)
Arabic reference (ES): Book 1, Hadith 195 (ES)