SAHIH BUKHARI

Volume 1, Book 4, Number 178:

Narrated by 'Ali
I used to get emotional urethral discharges frequently and felt shy to ask Allah's Apostle about it. So I requested Al-Miqdad bin Al-Aswad to ask (the Prophet ) about it. Al-Miqdad asked him and he replied, "On has to perform ablution (after it)."