Musnad Ahmad 2:84

Sufyan narrated to us, from Abdullah ibn Dinar, from Ibn Umar, from Umar, that he asked the Prophet, peace and blessings of Allah be upon him: "Does one of us sleep while he is in a state of janabah (major ritual impurity)?" He said: "He performs wudu (ablution) and sleeps if he wishes." And Sufyan said once: "Let him perform wudu and let him sleep."