Deuteronomy 19:6-8

New Revised Standard Version, Anglicised

⁶ But if the distance is too great, the avenger of blood in hot anger might pursue and overtake and put the killer to death, although a death sentence was not deserved, since the two had not been at enmity before. ⁷ Therefore I command you: You shall set apart three cities.

⁸ If the Lord your God enlarges your territory, as he swore to your ancestors—and he will give you all the land that he promised your ancestors to give you,