Numbers 35:13-17

So the cities which you are to provide shall be six cities of refuge for you.

You shall provide three cities across the Jordan, and three cities in the land of Canaan; they are to be cities of refuge.

These six cities shall be a refuge for the sons of Israel, for the stranger, and for the foreign resident among them; so that anyone who kills a person unintentionally may flee there.

‘But if he struck him with an iron object, so that he died, he is a murderer; the murderer must be put to death.

And if he struck him with a stone in the hand, by which he would die, and as a result he did die, he is a murderer; the murderer must be put to death.