Musannaf Ibn Abi Shayba 3:859

Yazid ibn Harun narrated to us, he said: Mansur ibn Hayyan informed us, he said: I heard ‘Amr ibn Maymun al-Awdi saying: I used to pray the dawn prayer behind ‘Umar ibn al-Khattab, and even if my son were three cubits away from me, I would not have recognized him until he spoke.