Musnad Ahmad 27:1048

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Abdullah ibn Dinar, I heard Ibn ‘Umar saying: ‘Umar asked the Messenger of Allah (may Allah bless him and grant him peace), “I become in a state of major ritual impurity (janabah) during the night, so what should I do?” He said, “Wash your private part, then perform ablution (wudu), then sleep.”