Numbers 35:11-15

11you must then designate some towns as towns of refuge for you, to which a person who has killed someone unintentionally may flee.

12And they must stand as your towns of refuge from the avenger in order that the killer may not die until he has stood trial before the community.

13These towns that you must give shall be your six towns for refuge.

14“You must give three towns on this side of the Jordan, and you must give three towns in the land of Canaan; they must be towns of refuge.

15These six towns will be places of refuge for the Israelites, and for the foreigner, and for the settler among them, so that anyone who kills any person accidentally may flee there.