Psalm 137:8 in the King James Version
O daughter of Babylon, who art to be destroyed; happy shall he be, that rewardeth thee as thou hast served us.
Context
7 Remember, LORD, against the children of Edom in the day of Jerusalem, who said, “Raze it! Raze it even to its foundation!”
8 Daughter of Babylon, doomed to destruction, he will be happy who repays you, as you have done to us.
9 Happy shall he be, who takes and dashes your little ones against the rock.