Deuteronomy 19:4-10

“Now this is the case of the offender (manslayer) who may escape there and live [protected from vengeance]: when he kills his neighbor unintentionally, not having hated him previously— as [for example] when a man goes into the forest with his neighbor to cut wood, and his hand swings the axe to cut down the tree, but the iron head slips off the wooden handle and hits his companion and he dies—the offender may escape to one of these cities and live; otherwise the avenger of blood might pursue the offender in the heat of anger, and overtake him, because it is a long way, and take his life, even though he did not deserve to die, since he did not hate his neighbor beforehand. Therefore, I command you, saying, ‘You shall set aside three cities [of refuge] for yourself.’ “If the LORD your God enlarges your border, as He has sworn to your fathers to do, and gives you all the land which He promised to give to your fathers— if you keep and carefully observe all these commandments which I am commanding you today, to love the LORD your God, and to walk [that is, to live each and every day] always in His ways—then you shall add three more cities [of refuge] for yourself, besides these three, so that innocent blood will not be shed [by blood avengers] in your land which the LORD your God is giving you as an inheritance, and blood guilt will not be on you [for the death of an innocent man].