Deuteronomy 4:41-49

Then Moses set apart three cities in the east beyond the Jordan, that the manslayer might flee there, anyone who kills his neighbor unintentionally, without being at enmity with him in time past; he may flee to one of these cities and save his life: Bezer in the wilderness on the tableland for the Reubenites, Ramoth in Gilead for the Gadites, and Golan in Bashan for the Manassites. This is the law that Moses set before the people of Israel. These are the testimonies, the statutes, and the rules, which Moses spoke to the people of Israel when they came out of Egypt, beyond the Jordan in the valley opposite Beth-peor, in the land of Sihon the king of the Amorites, who lived at Heshbon, whom Moses and the people of Israel defeated when they came out of Egypt. And they took possession of his land and the land of Og, the king of Bashan, the two kings of the Amorites, who lived to the east beyond the Jordan; from Aroer, which is on the edge of the Valley of the Arnon, as far as Mount Sirion (that is, Hermon), together with all the Arabah on the east side of the Jordan as far as the Sea of the Arabah, under the slopes of Pisgah.