The Messenger of Allah ﷺ said, "The son of a people's sister is one of them."
قال رسول الله ﷺ: ابن أخت القوم منهم.
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Abu Dawud (5122) narrated it from Abu Bakr bin Abu Shayba, who said, Abu Usama narrated to us, from Awf, from Ziyad bin Mikhraq, from Abu Kinana, from Abu Musa, and he related it.Ahmad (19541) narrated it through the route of Awf, and in it there occurs, The Messenger of Allah ﷺ stood at the door of a house in which there was a group of Quraysh, and he said, while holding the two sides of the doorframe, "Is there anyone in the house other than a man of Quraysh?" It was said, "Messenger of Allah, no one except so-and-so, the son of our sister." He said, "The sister's son of a people belongs to them." Then he said, "This matter belongs to Quraysh so long as, when appealed to for mercy, they show mercy, and when they judge, they are just, and when they divide, they act fairly. Whoever among them does not do this, upon him is the curse of Allah, the angels, and all the people, and neither ransom nor justice will be accepted from him."Its chain is hasan because of Abu Kinana, for two narrators reported from him as mentioned in Tahdhib, and no criticism has been transmitted concerning him, and his hadith has a firm basis.Haythami mentioned it in Majma (5/193) and said, "Ahmad, Bazzar, and Tabarani narrated it, and the men of Ahmad's narration are trustworthy."