The Suicide Squad novel actually included this scene. In the book, Harley Quinn asks “Why the favor, Bats?”, to which Batman replies: “Joker took something important away from me. It’s my turn.” That’s a clear reference to Robin, who was killed by the hands of The Joker. In the video above at the 20 second mark, you can tell that Ben Affleck is saying a variation of that line.
VIA: Batman News