Sahih Al Bukhari – Book of Bathing (Ghusl)

Volumn 001, Book 005, Hadith Number 285.
—————————————–
Narated By 'Umar bin Al-Khattab RA : I asked Allah's Apostle PBUH "Can any one of us sleep while he is Junub?" He replied, "Yes, if he performs ablution, he can sleep while he is Junub."