Numbers 35:14-18

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.

Or if he struck him with a wooden object 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.