Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[100] Now when Hadad, king of Damascus and of Syria, heard that David fought against Hadadezer, who was his friend, he came to his assistance with a powerful army, in hopes to rescue him; and when he had joined battle with David at the river Euphrates, he failed of his purpose, and lost in the battle a great number of his soldiers; for there were slain of the army of Hadad twenty thousand, and all the rest fled. Nicelens also [of Damascus] makes mention of this king in the fourth book of his histories; where he speaks thus: "A great while after these things had happened, there was one of that country whose name was Hadad, who was become very potent; he reigned over Damascus, and, the other parts of Syria, excepting Phoenicia. He made war against David, the king of Judea, and tried his fortune in many battles, and particularly in the last battle at Euphrates, wherein he was beaten. He seemed to have been the most excellent of all their kings in strength and manhood," Nay, besides this, he says of his posterity, that "they succeeded one another in his kingdom, and in his name;" where he thus speaks: "When Hadad was dead, his posterity reigned for ten generations, each of his successors receiving from his father that his dominion, and this his name; as did the Ptolemies in Egypt. But the third was the most powerful of them all, and was willing to avenge the defeat his forefather had received; so he made an expedition against the Jews, and laid waste the city which is now called Samaria." Nor did he err from the truth; for this is that Hadad who made the expedition against Samaria, in the reign of Ahab, king of Israel, concerning whom we shall speak in due place hereafter.