Muwatta Imam Malik (Riwayat Ibn al-Qasim)

And with this same chain (it is narrated from Sayyiduna Ibn Umar, may Allah be pleased with them both) that Sayyiduna Umar ibn al-Khattab, may Allah be pleased with him, informed the Messenger of Allah, peace and blessings be upon him, that he sometimes became junub (in a state of major ritual impurity) at night (so what should he do?). The Messenger of Allah, peace and blessings be upon him, said: "Perform wudu and wash your private part (penis), then go to sleep."