It is narrated from Sayyiduna Amr bin Awf al-Muzani (may Allah be pleased with him) that he said: I was sitting in the gathering of the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "The ally of a people (that is, one who has a pact of friendship and cooperation with a tribe) is counted as one of them, and the sister's son of a people is also regarded as one of them."
In the chain of this report, the narrator named Kathir bin Abdullah is da'if (weak); however, supporting reports of this hadith exist in Sahih Bukhari and Sahih Muslim, on account of which its original meaning is sahih and established.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب البر والصلة / 2551
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :إسناده صحيح. » «أخرجه مسند الدارمي برقم: 2570، وأخرجه سنن ابن ماجه برقم: 165، وأخرجه المطالب العالية لابن حجر برقم: 1534، وأخرجه المعجم الكبير للطبراني برقم: 2»