Musnad Ahmad 1153:1628

Muhammad ibn Bakr narrated to us, he said: Ibn Jurayj informed us, he said: Ibn Shihab informed me, from Abu Salamah, from Aisha, that the Prophet, peace and blessings of Allah be upon him, "when he wanted to sleep while he was in a state of major ritual impurity (junub), he would perform ablution (wudu) like his ablution for prayer."