I first encountered this famous remark of Heine's in Freud, who was discussing revenge; Heine wrote:

Mine is a most peaceable disposition.  My wishes are: a humble cottage with a thatched roof, but a good bed, good food, the freshest milk and butter, flowers before my window, and a few fine trees before my door; and if God wants to make my happiness complete, he will grant me the joy of seeing some six or seven of my enemies hanging from those trees.  Before death I shall, moved in my heart, forgive them all the wrong they did me in their lifetime.  One must, it is true, forgive one's enemies– but not before they have been hanged.