It was narrated from Ibn 'Umar that :
'Umar bin Khattab said to the Messenger of Allah: "can anyone of us sleep if he is sexually impure?" He said: "Yes, if he performs ablution." (DE)
English reference (DE): Vol. 1, Book 1, Hadith 585 (DE)
Arabic reference (DE): Book 1, Hadith 628 (DE)