Musannaf Ibn Abi Shayba 17:1026

Abu Bakr narrated to us, he said: Ibn ‘Ayyash narrated to us, from ‘Asim, from Abu al-‘Adbas, he said: I heard ‘Umar saying: "Frighten the vermin before they frighten you, practice archery, adopt the way of Ma‘add (i.e., live a rugged life), be rough/coarse, and make the head two heads (i.e., shave the head or keep it short). Separate yourselves from death (i.e., avoid places of plague or danger), do not linger in a land of incapacity (or helplessness), frighten the snakes before they frighten you, and improve your dwellings."