Deuteronomy 19:2-13

19:2 you must set apart for yourselves three cities in the middle of your land that the Lord your God is giving you as a possession. 19:3 You shall build a roadway and divide into thirds the whole extent of your land that the Lord your God is providing as your inheritance; anyone who kills another person should flee to the closest of these cities. 19:4 Now this is the law pertaining to one who flees there in order to live, if he has accidentally killed another without hating him at the time of the accident. 19:5 Suppose he goes with someone else to the forest to cut wood and when he raises the ax to cut the tree, the ax head flies loose from the handle and strikes his fellow worker so hard that he dies. The person responsible may then flee to one of these cities to save himself. 19:6 Otherwise the blood avenger will chase after the killer in the heat of his anger, eventually overtake him, and kill him, though this is not a capital case since he did not hate him at the time of the accident. 19:7 Therefore, I am commanding you to set apart for yourselves three cities. 19:8 If the Lord your God enlarges your borders as he promised your ancestors and gives you all the land he pledged to them, 19:9 and then you are careful to observe all these commandments I am giving you today (namely, to love the Lord your God and to always walk in his ways), then you must add three more cities to these three. 19:10 You must not shed innocent blood in your land that the Lord your God is giving you as an inheritance, for that would make you guilty. 19:11 However, suppose a person hates someone else and stalks him, attacks him, kills him, and then flees to one of these cities. 19:12 The elders of his own city must send for him and remove him from there to deliver him over to the blood avenger to die. 19:13 You must not pity him, but purge out the blood of the innocent from Israel, so that it may go well with you.