Numbers 35:16

The cities which you shall give shall be for you six cities of refuge.

You shall give three cities beyond the Jordan, and you shall give three cities in the land of Canaan. They shall be cities of refuge.

These six cities shall be refuge for the children of Israel, for the stranger, and for the foreigner living among them, that everyone who kills any person unwittingly may flee there.

If he struck him with a stone in the hand, by which a man may die, and he died, he is a murderer. The murderer shall surely be put to death.

Or if he struck him with a weapon of wood in the hand, by which a man may die, and he died, he is a murderer. The murderer shall surely be put to death.

The avenger of blood shall himself put the murderer to death. When he meets him, he shall put him to death.