Deuteronomy 19:3

paving the road carefully. And you shall divide the entire province of your land equally into three parts, so that he who is forced to flee because of manslaughter may have a place nearby to which he may be able to escape

Other versions

King James Version

Thou shalt prepare thee a way, and divide the coasts of thy land, which the LORD thy God giveth thee to inherit, into three parts, that every slayer may flee thither.

English Standard Version

You shall measure the distances and divide into three parts the area of the land that the LORD your God gives you as a possession, so that any manslayer can flee to them.

New International Version

Build roads to them and divide into three parts the land the LORD your God is giving you as an inheritance, so that anyone who kills a man may flee there.