(34) باب مَنْ لَمْ يَرَ الْوُضُوءَ إِلاَّ مِنَ الْمَخْرَجَيْنِ، مِنَ الْقُبُلِ وَالدُّبُرِ
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)."
Reference: Sahih al-Bukhari 178
In-book reference: Book 4, Hadith 44
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 4, Hadith 178