Musnad Ahmad 2:102

Yahya narrated to us, Husayn al-Mu‘allim narrated to us, ‘Amr ibn Shu‘ayb narrated to us, from his father, from his grandfather, who said: When ‘Amr returned, the sons of Ma‘mar ibn Habib came to dispute with him regarding the guardianship (wala’) of their sister before ‘Umar ibn al-Khattab. He said: "I will judge between you according to what I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'Whatever the child or the parent acquires, it belongs to his agnatic kin (asaba), whoever they may be.'" So he judged it for us accordingly.