Musnad Ahmad 1153:739

Mu'ammal narrated to us, he said: Hammad ibn Zayd narrated to us, he said: Hisham ibn 'Urwah narrated to us, from his father, from 'Aishah, she said: I said: "O Messenger of Allah, all of your wives have a kunyah (a patronymic name) except for me." He said: "Then take the kunyah of your son, 'Abdullah."