كتاب الحيض
3  
The Book of Menstruation
(4)
Chapter: Madhi (prostatic fluid)
(4)
باب الْمَذْىِ ‏
Sahih Muslim 303 a

'Ali reported:

I was one whose prostatic fluid flowed readily and I was ashamed to ask the Apostle (ﷺ) about it, because of the position of his daughter. I, therefore, asked Miqdad. b. al-Asad and he inquired of him (the Holy Prophet). He (the Holy Prophet) said: He should wash his male organ and perform ablution.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعٌ، وَأَبُو مُعَاوِيَةَ وَهُشَيْمٌ عَنِ الأَعْمَشِ، عَنْ مُنْذِرِ بْنِ يَعْلَى، - وَيُكْنَى أَبَا يَعْلَى - عَنِ ابْنِ الْحَنَفِيَّةِ، عَنْ عَلِيٍّ، قَالَ كُنْتُ رَجُلاً مَذَّاءً وَكُنْتُ أَسْتَحْيِي أَنْ أَسْأَلَ النَّبِيَّ صلى الله عليه وسلم لِمَكَانِ ابْنَتِهِ فَأَمَرْتُ الْمِقْدَادَ بْنَ الأَسْوَدِ فَسَأَلَهُ فَقَالَ ‏ "‏ يَغْسِلُ ذَكَرَهُ وَيَتَوَضَّأُ ‏"‏ ‏.‏
Reference : Sahih Muslim 303a
In-book reference : Book 3, Hadith 17
USC-MSA web (English) reference : Book 3, Hadith 593
  (deprecated numbering scheme)