Musnad Ahmad 1153:2182

Abu al-Qasim ibn Abi al-Zinad narrated to us, he said: Aflah informed me, from al-Qasim, from Aisha: "That the Messenger of Allah (peace and blessings of Allah be upon him) had intercourse with his wife, then he reached the morning and performed ghusl (ritual bath), and he prayed and fasted that day."