Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 221
Narated By 'Abd Allah b. 'Umar : 'Umar b. al-Khattab said to the Apostle of Allah (may peace be upon him) that he became sexually defiled at night (asking him what he should do). The Apostle of Allah (may peace be upon him) said: You should perform ablution and wash your penis and then sleep.