Musannaf Ibn Abi Shayba 36:518

Ja'far ibn 'Awn narrated to us, from Abu al-'Anbas, from Ibn Abi Mulaykah, who said: I heard 'Aishah—and she was asked, "O Mother of the Believers, whom did the Messenger of Allah, may Allah bless him and grant him peace, appoint as a successor, or whom would he have appointed?" She said: "Abu Bakr." It was said to her: "Then who?" She said: "Then 'Umar." It was said: "Who after 'Umar?" She said: "Abu 'Ubaydah ibn al-Jarrah."