Deuteronomy 19:9-11

9you must designate three additional cities of refuge. (He will give you this land if you are careful to obey all the commands I have given you—if you always love the Lord your God and walk in his ways.)

10That way you will prevent the death of innocent people in the land the Lord your God is giving you as your special possession. You will not be held responsible for the death of innocent people.

11“But suppose someone is hostile toward a neighbor and deliberately ambushes and murders him and then flees to one of the cities of refuge.