Numbers 21:23-25

23But Sihon would not let Israel travel through his territory. Instead, he gathered his whole army and went out to confront Israel in the wilderness. When he came to Jahaz, he fought against Israel.

24Israel struck him with the sword and took possession of his land from the Arnon to the Jabbok, but only up to the Ammonite border, because it was fortified.

25Israel took all the cities and lived in all these Amorite cities, including Heshbon and all its surrounding villages.