Numbers 35:15-17

New Revised Standard Version Catholic Edition

¹⁵ These six cities shall serve as refuge for the Israelites, for the resident or transient alien among them, so that anyone who kills a person without intent may flee there.

Concerning Murder and Blood Revenge

¹⁶ But anyone who strikes another with an iron object, and death ensues, is a murderer; the murderer shall be put to death. ¹⁷ Or anyone who strikes another with a stone in hand that could cause death, and death ensues, is a murderer; the murderer shall be put to death.