Musannaf Ibn Abi Shayba 9:1147

Ubaydullah narrated to us, from Isra'il, from Abu Ishaq, from al-Bara', that it was said to the Prophet (peace be upon him): "Do you have an interest in the daughter of Hamza?" He said: "She is not lawful for me; she is the daughter of my brother through breastfeeding."