Zubayr bin Awwam reported,

Allah revealed concerning us specifically, the people of Quraysh and the Ansar, "And those of kinship are more entitled to one another in the decree of Allah" [Anfal 8:75].He said, "That was because when we, the people of Quraysh, came to Madinah, we had no wealth, and we found the Ansar to be the best of brothers. So we entered into pacts of brotherhood with them and inherited from one another. Abu Bakr formed such a bond with Kharijah bin Zayd, Umar with so-and-so, and Uthman bin Affan with a man from Banu Zurayq bin Saad al-Zuraqi, though some people say it was someone else."Zubayr said, "I myself formed such a bond with Kaab bin Malik. They inherited from us and we inherited from them. On the day of Uhud, I was told, 'Your brother Kaab bin Malik has been killed.' I came to him and moved him, and I found that his weapons had weighed him down, as it appeared to us. By Allah, my son, had he died that day leaving this world behind, no one would have inherited from him but me, until Allah revealed this verse concerning us, the people of Quraysh and the Ansar specifically. Then we returned to our own kin as our heirs."

عن الزبير بن العوام قال

أنزل الله عز وجل فينا خاصة معشر قريش والأنصار {وأولوا الأرحام بعضهم أولى ببعض في كتاب الله} قال: وذلك أنا معشر قريش لما قدمنا المدينة ولا أموال لنا، فوجدنا الأنصار نعم الإخوان، فواخيناهم وأورثناهم، فآخى أبو بكر خارجة بن زيد، وآخى عمر فلانا، وآخى عثمان بن عفان رجلا من بني زريق بن سعد الزرقي ويقول بعض الناس: غيره، قال الزبير: وواخيت أنا كعب بن مالك، وأورثونا وأورثناهم، فلما كان يوم أحد قيل لي: قد قتل أخوك كعب بن مالك، فجئته، فانتقلته، فوجدت السلاح قد ثقله فيما نرى، فوالله يا بني لو مات يومئذ عن الدنيا ما ورثه غيري، حتى أنزل الله هذه الآية فينا معشر قريش والأنصار خاصة فرجعنا إلى مواريثنا.