Deuteronomy 19:3-5

Revised Standard Version

³ You shall prepare the roads, and divide into three parts the area of the land which the Lord your God gives you as a possession, so that any manslayer can flee to them.

⁴ “This is the provision for the manslayer, who by fleeing there may save his life. If any one kills his neighbor unintentionally without having been at enmity with him in time past— ⁵ as when a man goes into the forest with his neighbor to cut wood, and his hand swings the axe to cut down a tree, and the head slips from the handle and strikes his neighbor so that he dies—he may flee to one of these cities and save his life;