Musnad Ahmad 32:1377

Hashim narrated to us, Shu'bah narrated to us, from Mu'awiyah ibn Qurrah Abu Iyas, who said: I said to him: "I heard Anas narrating from the Prophet, may Allah bless him and grant him peace, that he said regarding al-Nu'man ibn Muqarrin: 'The son of a people's sister is one of them,' or 'is from among themselves.'" He said: "Yes."