It was narrated from 'Abdullah bin 'Umar that 'Umar said:
"O Messenger of Allah! May any one of us sleep while he is Junub?" He said: "When he performs Wudu'." (ES)
English reference (ES): Vol. 1, Book 1, Hadith 260 (ES)
Arabic reference (ES): Book 1, Hadith 261 (ES)