Musannaf Ibn Abi Shayba 17:1181

Waki’ narrated to us, from Shu’bah, from Qatadah, who said: I said to Mu’awiyah ibn Qurrah, "Did you hear Anas ibn Malik say that the Messenger of Allah (peace be upon him) said to al-Nu’man ibn Muqarrin, 'The sister’s son of a people is from among themselves'?" He said, "Yes."