It is narrated from Ubaid bin Abdullah bin Zam‘ah that his mother, Zainab bint Abi Salamah (may Allah be pleased with her), was breastfed by Asma bint Abi Bakr (may Allah be pleased with her), the wife of Zubair bin Al-Awwam (may Allah be pleased with him). Zainab bint Abi Salamah (may Allah be pleased with her) said: Zubair (may Allah be pleased with him) would come to me while I was combing my hair, and he would take hold of one of my braids and say, “Come, talk to me,” and I considered him my (foster) father and his sons as my brothers. Then, before the incident of Harrah, Abdullah bin Zubair (may Allah be pleased with them both) sent a marriage proposal for my daughter Umm Kulthum to Hamzah bin Zubair. Hamzah was from another wife (Kalbiyyah). Zainab said to the messenger of Ibn Zubair (may Allah be pleased with them both): “Is it permissible for her to marry him? For she is his niece.” Then Abdullah bin Zubair (may Allah be pleased with them both) again sent a messenger to me and said: “Hamzah is not your brother, for only those sons of Asma (may Allah be pleased with her) are your brothers, and those sons of Zubair (may Allah be pleased with him) from women other than Asma are not your brothers. Send someone to investigate this matter.” Zainab says: I sent messengers and also asked myself; at that time, many Companions (may Allah be pleased with them) and Mothers of the Believers were present. All of them told Zainab that nothing becomes unlawful (haram) from the man’s side through breastfeeding. Then Zainab married her daughter (Umm Kulthum) to Hamzah bin Zubair, and she remained in his marriage until his death.
Hadith Referenceمسند الإمام الشافعي / كتاب النكاح / 1186
Hadith Takhrijفي اسناده مقال فان أبا عبيدة بن عبد الله بن زمعة مقبول حيث يتابع ، ولم يتابع اخرجه البيهقي في المعرفة السنن والآثار (47090) ۔ والدارقطنی : (4 / 179 - 180)۔