“The ulterior motives with which you absorb and assimilate Evil are not your own but those of Evil.”

Source: White Oleander

This is a variant or paraphrase of The Paradoxical Commandments, by Kent M. Keith, student activist, first composed in 1968 as part of a booklet for student leaders, which had hung on the wall of Mother Teresa's children's home in Calcutta, India, and have sometimes become misattributed to her. The version posted at his site http://www.paradoxicalcommandments.com begins:
Misattributed
Context: People are often unreasonable and self-centered. Forgive them anyway. If you are kind, people may accuse you of ulterior motives. Be kind anyway. If you are honest, people may cheat you. Be honest anyway. If you find happiness, people may be jealous. Be happy anyway. The good you do today may be forgotten tomorrow. Do good anyway. Give the world the best you have and it may never be enough. Give your best anyway. For you see, in the end, it is between you and God. It was never between you and them anyway.

§ IV
1910s, At the Feet of the Master (1911)
Context: See what gossip does. It begins with evil thought, and that in itself is a crime. For in everyone and in everything there is good; in everyone and in everything there is evil. Either of these we can strengthen by thinking of it, and in this way we can help or hinder evolution; we can do the will of the Logos or we can resist Him. If you think of the evil in another, you are doing at the same time three wicked things:
(1) You are filling your neighbourhood with evil thought instead of with good thought, and so you are adding to the sorrow of the world.
(2) If there is in that man the evil which you think, you are strengthening it and feeding it; and so you are making your brother worse instead of better. But generally the evil is not there, and you have only fancied it; and then your wicked thought tempts your brother to do wrong, for if he is not yet perfect you may make him that which you have thought him.
(3) You fill your own mind with evil thoughts instead of good; and so you hinder your own growth, and make yourself, for those who can see, an ugly and painful object instead of a beautiful and lovable one.
Not content with having done all this harm to himself and to his victim, the gossip tries with all his might to make other men partners in his crime. Eagerly he tells his wicked tale to them, hoping that they will believe it; and then they join with him in pouring evil thought upon the poor sufferer. And this goes on day after day, and is done not by one man but by thousands. Do you begin to see how base, how terrible a sin this is? You must avoid it altogether.

28
The Zürau Aphorisms (1917 - 1918)

Source: I, Lucifer

Balsamo the Magician (or The Memoirs of a Physician) by Alex. Dumas (1891)

Question period following Lecture 11 of Leonard Peikoff's series "The Philosophy of Objectivism," 1976