Musannaf Ibn Abi Shayba 1:677

Mu'tamir ibn Sulayman narrated to us, from Ubayd Allah ibn Umar, from Nafi', from Ibn Umar, that Umar asked the Prophet, may Allah bless him and grant him peace: "I become in a state of janaba (major ritual impurity) and I wish to sleep." He said: "If you wish to sleep, then perform wudu (ablution)."