Judges 11:22

And they possessed all the coasts of the Amorites, from Arnon even unto Jabbok, and from the wilderness even unto Jordan.

Cross-reference

Deuteronomy 2:36 recounts the same conquest from Arnon to Gilead — confirming the extent of land God gave.

Joshua 12:2 lists Sihon's kingdom with identical geographic boundaries — confirming the territory Israel took.