Deuteronomy 19:6-8

Revised Standard Version

⁶ lest the avenger of blood in hot anger pursue the manslayer and overtake him, because the way is long, and wound him mortally, though the man did not deserve to die, since he was not at enmity with his neighbor in time past. ⁷ Therefore I command you, You shall set apart three cities. ⁸ And if the Lord your God enlarges your border, as he has sworn to your fathers, and gives you all the land which he promised to give to your fathers—