Musnad Ahmad 27:607

He said: I found in my father’s book: Yazid narrated to us, he said: Shu’bah informed us, from ‘Abdullah ibn Dinar, from Ibn ‘Umar, that ‘Umar said: O Messenger of Allah, I become in a state of major ritual impurity (janabah) during the night. He said: "Wash your private part, then perform ablution (wudu), then sleep."