Musannaf Ibn Abi Shayba 26:538

Sufyan ibn ‘Uyaynah narrated to us, from al-Zuhri, who heard Sinan Abu Jamilah say: I found a foundling during the time of ‘Umar, so my ‘arif (tribal leader) mentioned it to ‘Umar. He summoned me and asked me, so I informed him. He said: "He is free, his wala’ (right of inheritance/patronage) is yours, and his nursing is upon us."