Musannaf Ibn Abi Shayba 36:444

Muhammad ibn Ubayd narrated to us, he said: Wa'il ibn Dawud narrated to us, he said: I heard al-Bahiy narrating that: Aisha used to say: The Messenger of Allah (may Allah bless him and grant him peace) never sent Zayd ibn Harithah in an army at all, except that he appointed him over them. And had he remained after him, he would have appointed him as his successor.