Deuteronomy 3:16
And unto the Reubenites and unto the Gadites I gave from Gilead even unto the river Arnon half the valley, and the border even unto the river Jabbok, which is the border of the children of Ammon;
Cross-references
In Deuteronomy 2:37, the same Jabbok river border with Ammon is mentioned, directly echoing this verse's boundary.
In Numbers 21:24, the conquered Amorite land extends from Arnon to Jabbok—exactly the region given here.
In Numbers 32:33-38, this same land grant to Reuben and Gad is detailed, listing the cities they rebuilt.
In Joshua 12:2, Sihon's territory from Arnon to Jabbok matches the boundaries of the land given to Reuben and Gad.
In Joshua 13:9, the territory of Reuben and Gad is described with the same Arnon valley border, confirming the inheritance.
Joshua 22:9 explicitly states these tribes returned to the land 'according to the command of the LORD through Moses' — a direct citation of the grant in Deuteronomy 3:16.
In Judges 11:13, the Ammonite king claims the land from Arnon to Jabbok — exactly the area given to Reuben and Gad in Deuteronomy 3:16.