Musnad Ahmad 1153:1836

Hammad ibn Khalid narrated to us, he said: Aflah narrated to us, from al-Qasim, from Aisha, she said: The Messenger of Allah (peace and blessings of Allah be upon him) had intercourse with some of his wives, then he slept while he was in a state of janabah (major ritual impurity) until morning came. Then he performed ghusl (ritual bath) and fasted his day.