Deuteronomy 19:2–9

²then set aside for yourselves three cities in the land the Lord your God is giving you to possess. ³Determine the distances involved and divide into three parts the land the Lord your God is giving you as an inheritance, so that a person who kills someone may flee for refuge to one of these cities.

⁴This is the rule concerning anyone who kills a person and flees there for safety—anyone who kills a neighbor unintentionally, without malice aforethought. ⁵For instance, a man may go into the forest with his neighbor to cut wood, and as he swings his ax to fell a tree, the head may fly off and hit his neighbor and kill him. That man may flee to one of these cities and save his life. ⁶Otherwise, the avenger of blood^r might pursue him in a rage, overtake him if the distance is too great, and kill him even though he is not deserving of death, since he did it to his neighbor without malice aforethought. ⁷This is why I command you to set aside for yourselves three cities.

⁸If the Lord your God enlarges your territory,^s as he promised^t on oath to your ancestors, and gives you the whole land he promised them, ⁹because you carefully follow all these laws I command you today—to love the Lord your God and to walk always in obedience to him^u—then you are to set aside three more cities.