Musannaf Ibn Abi Shayba 27:401

Affan narrated to us, he said: Wuhayb and Hammad narrated to us, they said: Ubayd Allah ibn Uthman narrated to us, from Ibrahim, from Ikrimah, from Ibn Abbas regarding His saying: "Is he equal to one who commands justice and he is on a straight path?" He said: He is Uthman ibn Affan.