Mukhtasar Bukhari

Narrated Ibn Abbas (may Allah be pleased with them) that someone said to the Prophet (peace and blessings of Allah be upon him): Why do you not marry (the leader of the martyrs, Sayyiduna) Hamza's (may Allah be pleased with him) daughter? The Prophet (peace and blessings of Allah be upon him) replied: "She is my niece through breastfeeding."

Narrated from Ummul Momineen Aisha Siddiqa (may Allah be pleased with her) that she heard the voice of a man who was seeking permission to enter the house of Ummul Momineen Hafsa (may Allah be pleased with her). Ummul Momineen Aisha (may Allah be pleased with her) said: "O Messenger of Allah, indeed this (non-mahram) man wants to enter your house." So the Prophet Muhammad (peace and blessings be upon him) said: "I know that this is so-and-so, who is Hafsa's (may Allah be pleased with her) foster uncle." Aisha (may Allah be pleased with her) asked: "If so-and-so, who was my uncle through milk relationship, were alive, would I appear before him?" The Prophet (peace and blessings be upon him) said: "Yes! The relationships that are forbidden by lineage are also forbidden by suckling (milk relationship)."

Umm al-Mu’minin Umm Habibah bint Abi Sufyan (may Allah be pleased with her) says: I said, “O Messenger of Allah! Marry my sister, the daughter of Abu Sufyan.” He asked, “Do you like that?” (Do you not dislike having a co-wife?) I said, “Yes.” (But) even now, I am not your only wife, and I do not dislike my sister sharing goodness with me.” He said, “It is not lawful for me (to have two sisters in marriage at the same time).” I said, “We have heard that you want to marry the daughter of Abu Salamah?” The Prophet (peace be upon him) asked, “The daughter of Umm Salamah? (Do you mean I want to marry her?)” I said, “Yes.” So the Prophet (peace be upon him) said, “Even if she were not my stepdaughter (the daughter of my wife from a previous husband), she would still not be lawful for me, because she is my niece through breastfeeding. Both Abu Salamah (her father) and I were breastfed by Thuwaibah (may Allah be pleased with her). (O lady!) Do not present your sisters and daughters to me (they are not lawful for me).”