Musnad Ahmad 1153:2372

Husayn ibn Muhammad narrated to us, he said: Al-Fudayl—meaning Ibn Sulayman—narrated to us, he said: Khuthaym ibn 'Arak narrated to us, from Sulayman ibn Yasar, from 'Aishah, she said: "The Messenger of Allah (peace and blessings of Allah be upon him) would wake up in a state of janabah (major ritual impurity) from intercourse, then he would perform ghusl (ritual bath), and then he would wake up fasting."