“What if your enemy were your enemy because of poor communication and misunderstanding? What if your enemy were your enemy because of the instigative nature of the ego? What if your enemy were a necessary obstacle put in your life by fate to overcome in order to progress to the higher version of self? I wonder about that because what if your enemy is in fact your hero? Make sure the snake in your life isn't just your pride and ego.”

Source: Lyonesse Trilogy (1983-1989), The Green Pearl (1985), Chapter 8, section 3 (p. 480)

1950s, Loving Your Enemies (November 1957)
Context: Now there is a final reason I think that Jesus says, "Love your enemies." It is this: that love has within it a redemptive power. And there is a power there that eventually transforms individuals. That’s why Jesus says, "Love your enemies." Because if you hate your enemies, you have no way to redeem and to transform your enemies. But if you love your enemies, you will discover that at the very root of love is the power of redemption. You just keep loving people and keep loving them, even though they’re mistreating you. Here’s the person who is a neighbor, and this person is doing something wrong to you and all of that. Just keep being friendly to that person. Keep loving them. Don’t do anything to embarrass them. Just keep loving them, and they can’t stand it too long. Oh, they react in many ways in the beginning. They react with bitterness because they’re mad because you love them like that. They react with guilt feelings, and sometimes they’ll hate you a little more at that transition period, but just keep loving them. And by the power of your love they will break down under the load. That’s love, you see. It is redemptive, and this is why Jesus says love. There’s something about love that builds up and is creative. There is something about hate that tears down and is destructive. So love your enemies.

This is sometimes attributed to Sun Tzu in combination with the above quote, as well as alone, but it too has not been sourced to any published translation of The Art of War, though it is similar in concept to his famous statement in Ch. 3 : "It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles..."
Misattributed

Source: The Goblin Quest Series, Goblin Hero (2007), Chapter 7 (p. 117)

1990s, Long Walk to Freedom (1995)

Source: Last Sacrifice

http://www.qern.org/ur/%D8%A7%D8%B3%D9%84%D8%A7%D9%85-%D8%B2%D9%86%D8%AF%DB%81-%DB%81%D9%88%D8%AA%D8%A7-%DB%81%DB%92-%DB%81%D8%B1-%DA%A9%D8%B1%D8%A8%D9%84%D8%A7-%DA%A9%DB%92-%D8%A8%D8%B9%D8%AF/
Describing some Muslim preachers who try to sell the utopia of a perfect Islamic society.

Source: Station Eleven (2014), Chapter 23 (p. 139)