Musnad Ahmad 1156:193

Rawh narrated to us, he said: Salih narrated to us, Ibn Shihab narrated to us, from Abu Bakr ibn Abd al-Rahman, from his father, from Aisha, that she informed him: "That the Messenger of Allah, peace and blessings of Allah be upon him, would wake up in a state of janabah (major ritual impurity) in Ramadan from his wives, then he would perform ghusl (ritual bath), and fast."