Musnad Ahmad 1153:865

Musa ibn Dawud narrated to us, he said: Ibn Lahi'ah narrated to us, from Abu al-Zubayr, from Jabir, that Abu 'Amr, the freed slave of 'Aishah, informed him, from 'Aishah, that she informed him: "That the Prophet, peace and blessings of Allah be upon him, would be in a state of major ritual impurity (junub) and would want to sleep, so he would perform ablution (wudu) like his ablution for prayer, then he would sleep."