Midrasch zu Schemuel II 8:3

II) On his way to restore his monument at the River [Euphrates] (II Samuel 8:3). It is written lacking in the book of Samuel, for this verse is mentioned in two places — in Samuel and Chronicles (I Chronicles 18:3), and the verse is said in two times and regarding two occasions (matters). Firstly it says to restore his monument at the river, and secondly to set up his monument at the river Euphrates. Though it is not the business of the first time to make known if it is the Euphrates or the Nile, it was written elsewhere, so Euphrates is read.

When David reigned, he wished to come into the land of Edom, but he was unable on account of the power of the covenant of Jacob's oath until he had broken that pillar. Concerning this, Solomon said: "And break in pieces their pillars" (Ex. 23:24). Afterwards he conquered the land of Edom, as it is said, "David smote also Hadadezer the son of Rehob, king of Zobah, as he went to recover his dominion at the river" (2 Sam. 8:3).