Musnad Abu Ya'la al-Mawsili 115:367

Ahmad ibn Ibrahim al-Dawraqi narrated to us, Bahz ibn Asad narrated to us, Shu'bah narrated to us, Qatadah narrated to us, [who said] Anas ibn Malik informed me that the Messenger of Allah (may Allah bless him and grant him peace) gathered the Ansar. He said, "Is there anyone among you who is not of you?" They said, "No, except for a son of a sister of ours." The Messenger of Allah (may Allah bless him and grant him peace) said, "The son of a people's sister is of themselves," or he said, "of the people."