Musar do Przysłów 5:9

And you, son of man, examine yourself and be far from cruelty and have mercy upon the poor and the needy and let the poor be as the members of your family. "Then the Lord … will show you mercy and have compassion upon you and multiply you" (Deut. 13:18). Everyone who has mercy on his fellow creatures will have mercy shown him from heaven (Shabbath 151b). Therefore, do not remove mercy from you but guard yourself against the quality of cruelty. And Solomon said: "Lest you give to others your vigour and your years unto the cruel (to being cruel)" (Prov. 5:9). And guard yourself against the desire for vengeance which itself stems from cruelty. If you wish to truly avenge yourself on your enemy then add to your good qualities and walk in the path of the upright, and in this way you will be avenged on him who hates you, for he will writhe in pain because of your good qualities and good repute and mourn when he hears good of you. But if you do ugly deeds then your enemy will rejoice over your shame and disgrace and thus avenge himself against you.