Musannaf Ibn Abi Shayba 21:117

Ubaydah ibn Humayd narrated to us, from Mansur, from Ibrahim, from Aisha, who said: I looked for the Messenger of Allah (peace and blessings of Allah be upon him) one night, but I did not find him. She said: So I thought that he had gone to some of his slave-girls or his wives. She said: Then I saw him while he was prostrating, and he was saying: "O Allah, forgive me for what I have kept secret and what I have made public."