Musnad Ahmad 1153:1579

Waki’ narrated to us, from Shu’bah, and Muhammad, who said: Shu’bah narrated to us, from al-Hakam, from Ibrahim, who said: Muhammad said: I heard Ibrahim, from al-Aswad, from ‘Aishah, that the Prophet, peace and blessings of Allah be upon him, "when he wanted to sleep or eat while he was in a state of major ritual impurity (junub), he would perform ablution (wudu)."