Deuteronomy 19:2–10

²then you are to set apart for yourselves three cities within the land that the LORD your God is giving you to possess. ³You are to build roads for yourselves^a and divide into three regions the land that the LORD your God is giving you as an inheritance, so that any manslayer can flee to these cities.

⁴Now this is the situation regarding the manslayer who flees to one of these cities to save his life, having killed his neighbor accidentally, without intending to harm him: ⁵If he goes into the forest with his neighbor to cut timber and swings his axe to chop down a tree, but the blade flies off the handle and strikes and kills his neighbor, he may flee to one of these cities to save his life.

⁶Otherwise, the avenger of blood might pursue the manslayer in a rage, overtake him if the distance is great, and strike him dead though he did not deserve to die, since he did not intend any harm. ⁷This is why I am commanding you to set apart for yourselves three cities.

⁸And if the LORD your God enlarges your territory, as He swore to your fathers, and gives you all the land He promised them, ⁹and if you carefully keep all these commandments I am giving you today, loving the LORD your God and walking in His ways at all times, then you are to add three more cities to these three.

¹⁰Thus innocent blood will not be shed in the land that the LORD your God is giving you as an inheritance, so that you will not be guilty of bloodshed.