Musnad Abu Ya'la al-Mawsili 3:122

Ishaq ibn Isma'il al-Taliqani narrated to us, Waki' narrated to us, from Shu'bah, from Abu 'Awn, from Abu Salih al-Hanafi, who said: Ali said while on the pulpit—and Ibn al-Kawwa' asked him about the daughter of a brother through breastfeeding—Ali said: I mentioned to the Messenger of Allah, peace and blessings of Allah be upon him, the daughter of Hamzah. He said: "Do you not know that she is the daughter of my brother through breastfeeding?"