Numbers 35:12-15

12The cities shall be to you as a refuge from the avenger, so that the one who has caused the death of another will not be killed until he has had a [fair] trial before the congregation.

13The cities which you are to provide shall be your six cities of refuge.

14You shall provide three cities on this [east] side of the Jordan [River], and three [more] cities in the land of Canaan; they are to be the cities of refuge.

15These six cities shall be a refuge for the Israelites and for the stranger and the resident alien among them; so that anyone who kills a person unintentionally may escape there.