Numbers 21:23-25

23But King Sihon refused to let them cross his territory. Instead, he mobilized his entire army and attacked Israel in the wilderness, engaging them in battle at Jahaz.

24But the Israelites slaughtered them with their swords and occupied their land from the Arnon River to the Jabbok River. They went only as far as the Ammonite border because the boundary of the Ammonites was fortified.

25So Israel captured all the towns of the Amorites and settled in them, including the city of Heshbon and its surrounding villages.