It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the daughter of Sayyiduna Hamzah (may Allah be pleased with him) was mentioned to the Prophet of Allah (peace and blessings be upon him), and her beauty was described, so the Messenger of Allah (peace and blessings be upon him) said: "Do you not know that she is my brother's daughter through breastfeeding? Do you not know that Allah Almighty has made unlawful through breastfeeding the same as He has made unlawful through lineage?"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10651