"We have been saying that you want to marry Durrah bint Abi Salamah." The Messenger of Allah said: "As a co-wife to Umm Salamah? Even if I were not married to Umm Salamah, she would not be permissible to me, for her father is my brother through breast-feeding."
Sunan an-Nasa'i Book 26, Hadith 91
← Previous Hadith "O Messenger of Allah, marry the daughter of my father" - meaning her sister. The Messenger of Allah said: "Would you like that?" She said: "Yes; I do not have you all to myself, and I would like to share this goodness with my sister." The Prophet said: "That is not permissible for me." Umm Habibah said: "O Messenger of Allah, by Allah, we have been saying that you want to marry Durrah bint Abi Salamah." He said: "The daughter of Umm Salamah?" I said: "Yes." He said: "By Allah, even if she were not my stepdaughter who is in my care, she would not be permissible for me (to marry), because she is the daughter of my brother through breast-feeding. Thuwaibah breastfed Abu Salamah and I. So do not offer your daughters or sisters to me in marriage."

Sunan an-Nasa'i Book 26, Hadith 90 Next Hadith → "O Messenger of Allah, what do you think of my sister?" He said: "What for?" She said: "For marriage." He said: "Would you like that?" She said: "Yes; I do not have you all to myself, and I would like to share this goodness with my sister." He said: "She is not permissible for me (to marry)." She said: "But I heard that you want to marry Durrah, the daughter of Umm Salamah." He said: "The daughter of Umm Salamah?" She said: "Yes." He said: "By Allah, even if she were not my stepdaughter she would not be permissible for me (to marry), because she is the daughter of my brother through breast-feeding. Do not offer your daughters and sisters to me in marriage."

Sunan an-Nasa'i Book 26, Hadith 92