Numbers 21:23-25

23But Sihon would not let Israel pass through his territory. He mustered his entire army and marched out into the wilderness against Israel. When he reached Jahaz, he fought with Israel.

24Israel, however, put him to the sword and took over his land from the Arnon to the Jabbok, but only as far as the Ammonites, because their border was fortified.

25Israel captured all the cities of the Amorites and occupied them, including Heshbon and all its surrounding settlements.