Numbers 35:14-16  American Standard Version

¹⁴ Ye shall give three cities beyond the Jordan, and three cities shall ye give in the land of Canaan; they shall be cities of refuge. ¹⁵ For the children of Israel, and for the stranger and for the sojourner among them, shall these six cities be for refuge; that every one that killeth any person ^[a]unwittingly may flee thither.

¹⁶ But if he smote him with an instrument of iron, so that he died, he is a murderer: the murderer shall surely be put to death.