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'." (RU)
English reference (RU): Vol. 1, Book 1, Hadith 260 (RU)
Arabic reference (RU): Book 1, Hadith 261 (RU)