Musnad Ahmad 724:1

Waki’ narrated to us, from Sufyan, from Ibn Khuthaym, from Isma’il ibn ‘Ubayd ibn Rifa’ah, from his father, from his grandfather, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The freed slave of a people is one of them, and the son of their sister is one of them, and their ally is one of them."