Midrash sur Rois 2 2:19

(Ib., ib., ib.) And tore of them forty and two boys. Said R. Jose, the son of R. Chanina: "On account of the forty-two sacrifices that Ballak, the king of Moab. offered, it happened that forty-two Israelites' children were torn." Is this the real cause? Behold R. Juda said in the name of Rab: "Always shall a man occupy himself with the study of the Torah, and the fulfillment of meritorious deeds, even it is not for its real purpose, because out of a selfish purpose he will come to do so for its real purpose, for as reward for the forty-two sacrifices that Ballak, the king of Moab offered, he was rewarded that Ruth came forth from him of whom Solomon is a descendant, concerning whom the passage says (I Kings 3, 4) One thousand burnt-offerings did Solomon offer upon the altar, and R. Jose, son of R. Chanina said: "Ruth was the daughter of King Eglon, who was the grandson of Ballak, the king of Moab." [Hence I see that at the end he meant well]. However, since his real purpose was to curse Israel, thus through the above incident his curse was fulfilled. (II Kings 2, 19) And the men of the city said unto Elisha, 'Behold, we pray thee; the situation of this city is pleasant, as my Lord seeth; but the water is bad, and the land causes miscarriages.' Since the water is bad and the land causes miscarriages why do they say that the city is splendid? Said R. Chanin: "It is the usual esteem in which inhabitants hold their place."