She told her that she once said to the Messenger of Allah ﷺ, "Messenger of Allah, marry my sister Azza."The Messenger of Allah ﷺ asked, "Would you really like that?"She replied, "Yes, Messenger of Allah. I am not your only wife, and I would love for my sister to share with me in something good."The Messenger of Allah ﷺ said, "She is not lawful for me."She said, "I said, 'Messenger of Allah, we have been hearing that you intend to marry Durra, the daughter of Abu Salama.'"He asked, "The daughter of Abu Salama?"She said, "Yes."The Messenger of Allah ﷺ said, "Even if she were not my stepdaughter raised under my care, she still would not be lawful for me. She is the daughter of my brother through nursing. Thuwayba nursed both me and Abu Salama. So do not offer me your daughters or your sisters in marriage."
حدثتها أنها قالت لرسول الله ﷺ يا رسول الله! انكح أختي عزة. فقال رسول الله ﷺ: أتحبين ذلك؟ فقالت: نعم. يا رسول الله! لست لك بمخلية. وأحب من شركني في خير أختي، فقال رسول الله ﷺ: فإن ذلك لا يحل لي قالت: فقلت: يا رسول الله! فإنا نتحدث أنك تريد أن تنكح درة بنت أبي سلمة. قال: بنت أبي سلمة؟ قالت: نعم. قال رسول الله ﷺ: لو أنها لم تكن ربيبتي في حجري ما حلت لي. إنها ابنة أخي من الرضاعة، أرضعتني وأبا سلمة ثويبة. فلا تعرضن علي بناتكن ولا أخواتكن.
Muslim narrated it in the Book of Suckling (16/1449) from Muhammad bin Rumh bin Muhajir, [who said] Layth informed us, from Yazid bin Abu Habib, that Muhammad bin Shihab wrote mentioning that Urwa told him, that Zaynab bint Abu Salama told him, that Umm Habiba, wife of the Prophet ﷺ, told her, and he mentioned it.Bukhari narrated it in the Book of Marriage (5107) through the hadith of Layth, from Aqeel, from Ibn Shihab, with his chain, similarly, but he did not name "Izza."Muslim said, "None of them named 'Izza' in his narration except Yazid bin Abu Habib."Her saying "mukhliya" is an active participle from "ikhlaa," meaning, she is not exclusively alone with you, nor free from a co-wife.Perhaps Umm Habiba did not know of the prohibition against combining two sisters in marriage, mentioned in Allah's saying, "and that you combine two sisters [in marriage]" [Nisa 4:23].