Musannaf Ibn Abi Shayba 28:88

Waki’ narrated to us, he said: Sufyan narrated to us, from Abu Ishaq, from Hassan bin Fa’id al-‘Absi, who said: Umar said: Courage and cowardice are instincts in men. The courageous man fights for those he knows and those he does not know. And the coward flees from his father and his mother.