Sahih al-Bukhari
Sahih al-Bukhari 178
Whosoever considers not to repeat ablution except if something is discharged or passed from exit (front or back private parts)
Arabic hadith text
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ مُنْذِرٍ أَبِي يَعْلَى الثَّوْرِيِّ، عَنْ مُحَمَّدٍ ابْنِ الْحَنَفِيَّةِ، قَالَ قَالَ عَلِيٌّ كُنْتُرَجُلاً مَذَّاءً، فَاسْتَحْيَيْتُ أَنْ أَسْأَلَ رَسُولَ اللَّهِ صلى الله عليه وسلم فَأَمَرْتُ الْمِقْدَادَ بْنَ الأَسْوَدِ فَسَأَلَهُ فَقَالَ " فِيهِ الْوُضُوءُ ". وَرَوَاهُ شُعْبَةُ عَنِ الأَعْمَشِ
Translation
Narrated `Ali
I used to get emotional urethral discharges frequently and felt shy to ask Allah's Messenger (ﷺ) about it. So I requested Al-Miqdad bin Al-Aswad to ask (the Prophet (ﷺ) ) about it. Al-Miqdad asked him and he replied, "One has to perform ablution (after it)."