Musannaf Ibn Abi Shayba 36:445

Muhammad ibn Ubayd narrated to us, he said: Isma'il narrated to us, from Mujalid ibn Sa'id, from 'Amir, that: 'Aisha used to say: "If Zayd were alive, the Messenger of Allah (may Allah bless him and grant him peace) would have appointed him as his successor."