It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that a man said: O Messenger of Allah, can one of us sleep while in a state of janabah? He (peace and blessings be upon him) said: "Yes, after performing ablution."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 965