Musnad Ahmad 2:34

Abu al-Yaman narrated to us, Abu Bakr narrated to us, from Hakim ibn Umayr and Damrah ibn Habib, they both said: Umar ibn al-Khattab said: "Whoever is pleased to look at the guidance of the Messenger of Allah, may Allah bless him and grant him peace, then let him look at the guidance of Amr ibn al-Aswad."