Deuteronomy 4:41-43

41Then Moses set apart three cities [of refuge] beyond the Jordan toward the rising of the sun (eastward),

42so that someone who committed manslaughter could flee there, [that is, a person] who killed his neighbor unintentionally and without previously having hostility toward him, and that by escaping to one of these cities he might [claim the right of asylum and] save his life:

43Bezer in the wilderness on the plateau for the Reubenites, and Ramoth in Gilead for the Gadites, and Golan in Bashan for the Manassites.