Sahih Bukhari
Bathing (Ghusl)
Volume: 001 / Book Number: 005 / Hadith Number: 288
Narrated 'Abdullah bin 'Umar:
Umar bin Al-Khattab told Allah's Apostle, "I became Junub at night." Allah's Apostle replied, "Perform ablution after washing your private parts and then sleep."