Deuteronomy 4:41-43

41Then Moses set apart three cities on the side of Jordan toward the sunrising; 42That the slayer might flee there, who should kill his neighbour unintentionally, and when he had not hated him in times past; and that fleeing to one of these cities he might live: 43Namely, Bezer in the wilderness, in the plain country, of the Reubenites; and Ramoth in Gilead, of the Gadites; and Golan in Bashan, of the Manassites.