"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.'" (Using translation from Nasāʾī 193)   

رَسُولُ اللهِ ﷺ لَا تَفْعَلْ إِذَا رَأَيْتَ الْمَذْيَ فَاغْسِلْ ذَكَرَكَ وَتَوَضَّأْ وُضُوءَكَ لِلصَّلَاةِ فَإِذَا نَضَحْتَ الْمَاءَ فَاغْتَسِلْ  

[Machine] From Umar ibn al-Khattab and Abdullah ibn Umar about the adulterer and its likes.  

عَنْ عُمَرَ بْنِ الْخَطَّابِ وَعَبْدِ اللهِ بْنِ عُمَرَ فِي الْمَذْيِ نَحْوَهُ