It is narrated from Sayyiduna Umar (may Allah be pleased with him) that he asked the Messenger of Allah (peace and blessings be upon him): "May one of us sleep while in a state of major ritual impurity (janabah)?" He (peace and blessings be upon him) said: "Yes, but let him perform ablution (wudu) like his ablution for prayer."
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 79