וַיַּ֣ךְ דָּוִ֔ד אֶת־הֲדַדְעֶ֥זֶר בֶּן־רְחֹ֖ב מֶ֣לֶךְ צוֹבָ֑ה בְּלֶכְתּ֕וֹ לְהָשִׁ֥יב יָד֖וֹ בִּֽנְהַר־[פְּרָֽת׃]
David smote also Hadadezer the son of Rehob, king of Zobah, as he went to establish his dominion at the river Euphrates.
Rashi on II Samuel
To enlarge his border. As [Yonasan] translates, "To widen his border," [Haddadezer] conquored land outside his countries border and widened his border.