Musnad Abu Ya'la al-Mawsili 3:119

Zuhayr narrated to us, Abu Mu'awiyah narrated to us, al-A'mash narrated to us, from Sa'd ibn 'Ubaydah, from Abu 'Abd al-Rahman al-Sulami, from 'Ali, who said: I said, "O Messenger of Allah, why do you choose [a wife] from Quraysh and leave us?" He said, "Do you have anyone?" I said, "Yes, the daughter of Hamzah." The Prophet, peace and blessings of Allah be upon him, said, "She is not lawful for me; she is only the daughter of my brother through breastfeeding."