Deuteronomy 19:3

1When the LORD your God cuts off the nations whose land the LORD your God gives you, and you succeed them and dwell in their cities and in their houses,

2you shall set apart three cities for yourselves in the middle of your land, which the LORD your God gives you to possess.

3You shall prepare the way, and divide the borders of your land which the LORD your God causes you to inherit into three parts, that every man slayer may flee there.

4This is the case of the man slayer who shall flee there and live: Whoever kills his neighbor unintentionally, and didn’t hate him in time past—

5as when a man goes into the forest with his neighbor to chop wood and his hand swings the ax to cut down the tree, and the head slips from the handle and hits his neighbor so that he dies—he shall flee to one of these cities and live.

6Otherwise, the avenger of blood might pursue the man slayer while hot anger is in his heart and overtake him, because the way is long, and strike him mortally, even though he was not worthy of death, because he didn’t hate him in time past.

7Therefore I command you to set apart three cities for yourselves.