John Gill Commentary Deuteronomy 4:46

"beyond the Jordan, in the valley over against Beth-peor, in the land of Sihon king of the Amorites, who dwelt at Heshbon, whom Moses and the children of Israel smote, when they came forth out of Egypt." — Deuteronomy 4:46 (ASV)

On this side Jordan, in the valley, over against Bethpeor ,
&c.] Where the Israelites abode some time; see (Deuteronomy 3:29) ,

in the land of Sihon king of the Amorites, who dwelt at Heshbon ;
which was now conquered, and in the hands of the Israelites:

whom Moses and the children of Israel smote, after they came out of
Egypt ;
not as soon as, or quickly after they came from thence; for it was but a few months ago since this conquest was made, whereas it was near forty years since they came out of Egypt.