The Book of Purification
1/130. Chapter:
Ghusl From (The Emission Of) Semen
Sunan an-Nasai
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 (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.'"
Reference : Sunan an-Nasa'i 193In-book reference : Book 1, Hadith 194English translation : Vol. 1, Book 1, Hadith 193