It was narrated that ‘Ali (رضي الله عنه) said: I was a man who emitted a great deal of madhi, but I felt too shy to ask the Messenger of Allah (ﷺ) because of his daughter, so I told Al-Miqdad to ask the Messenger of Allah (ﷺ) about a man who finds madhi. He said: `That is the water of the male, and every male has water, so let him wash his private part and testicles and do wudoo’ as for prayer.`
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا يَزِيدُ، أَنْبَأَنَا شَرِيكٌ، عَنِ الرُّكَيْنِ بْنِ الرَّبِيعِ، عَنْ حُصَيْنِ بْنِ قَبِيصَةَ، عَنْ عَلِيٍّ، قَالَ كُنْتُ رَجُلًا مَذَّاءً فَاسْتَحْيَيْتُ أَنْ أَسْأَلَ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مِنْ أَجْلِ ابْنَتِهِ فَأَمَرْتُ الْمِقْدَادَ فَسَأَلَ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَنْ الرَّجُلِ يَجِدُ الْمَذْيَ فَقَالَ ذَلِكَ مَاءُ الْفَحْلِ وَلِكُلِّ فَحْلٍ مَاءٌ فَلْيَغْسِلْ ذَكَرَهُ وَأُنْثَيَيْهِ وَلْيَتَوَضَّأْ وُضُوءَهُ لِلصَّلَاةِ.
sunnah.com