الرضاع
‘Abdullāh ibn ‘Abbās (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said about Hamzah's daughter: "It is unlawful for me to marry her. What is unlawful through lineage is also unlawful through breastfeeding, and she is the daughter of my brother from breastfeeding."
عن عبد الله بن عباس -رضي الله عنهما- «قال رسول الله -صلى الله عليه وسلم- في بنت حمزة: لا تحل لي، يحرم من الرضاع: ما يحرم من النسب، وهي ابنة أخي من الرضاعة».
شرح الحديث :
‘Ali ibn Abi Tālib (may Allah be pleased with him) desired that the Prophet (may Allah's peace and blessings be upon him) would marry the daughter of their uncle Hamzah, but the Prophet informed him that she is not lawful for him to marry because she is the daughter of his brother by breastfeeding. The Prophet and Hamzah were both breastfed by Thuwaybah, the maid servant of Abu Lahab. Therefore, Hamzah became his brother by breastfeeding and the Prophet is the paternal uncle of Hamzah's daughter and cannot marry her. Marriage that is permanently unlawful because of blood relationship is also permanently unlawful due to breastfeeding.