Plutarch De Vitioso Pudore 13

[13] But to proceed to another head, we must perform all reasonable and good offices to those that deserve them, not forced thereto by fear of shame, but cheerfully and readily. But where any thing prejudicial or unhandsome is required of us, we ought to remember the story that is related of Zeno. Meeting a young man of his acquaintance that slunk away under a wall, as if he would not be seen, and having learned from him that he withdrew from a fiend that importuned him to perjure himself, What, replied he, you novice! is that fellow not afraid or ashamed to require of thee what is unreasonable and unjust, and darest thou not stand against him in that which is just and honest? For he that first started that doctrine, that knavery is the best defence against a knave, was but an ill teacher, advising us to keep off wickedness by imitating it. But for such as presume upon our modesty, to keep them off with their own weapons, and not gratify their unreasonable impudence with an easy compliance, is but just and good, and the duty of every wise man.