Deuteronomy 19:4-10

“And this is the case of the manslayer who flees there, that he may live: Whoever kills his neighbor unintentionally, not having hated him in time past— as when a man goes to the woods with his neighbor to cut timber, and his hand swings a stroke with the ax to cut down the tree, and the head slips from the handle and strikes his neighbor so that he dies—he shall flee to one of these cities and live; lest the avenger of blood, while his anger is hot, pursue the manslayer and overtake him, because the way is long, and kill him, though he was not deserving of death, since he had not hated the victim in time past. Therefore I command you, saying, ‘You shall separate three cities for yourself.’ “Now if the LORD your God enlarges your territory, as He swore to your fathers, and gives you the land which He promised to give to your fathers, and if you keep all these commandments and do them, which I command you today, to love the LORD your God and to walk always in His ways, then you shall add three more cities for yourself besides these three, lest innocent blood be shed in the midst of your land which the LORD your God is giving you as an inheritance, and thus guilt of bloodshed be upon you.