أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، وَعَلِيُّ بْنُ حُجْرٍ، - وَاللَّفْظُ لِقُتَيْبَةَ - قَالَ حَدَّثَنَا عَبِيدَةُ بْنُ حُمَيْدٍ، عَنِ الرُّكَيْنِ بْنِ الرَّبِيعِ، عَنْ حُصَيْنِ بْنِ قَبِيصَةَ، عَنْ عَلِيٍّ، - رضى الله عنه - قَالَ كُنْتُ رَجُلاً مَذَّاءً فَقَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ إِذَا رَأَيْتَ الْمَذْىَ فَاغْسِلْ ذَكَرَكَ وَتَوَضَّأْ وُضُوءَكَ لِلصَّلاَةِ وَإِذَا فَضَخْتَ الْمَاءَ فَاغْتَسِلْ ‏"‏ ‏.‏

It was narrated that 'Ali said: "I was one who had a lot of prostatic discharge, and the Messenger of Allah (PBUH) 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.'" Translation Not Available

Book Ref: Sunan An Nisai Book 1 Hadith 193
Web Ref:  Sunan An Nisai Not Available