Shemiras Halashon Halachos

Hilchos Rechilus, chapter 1, section 10

Crafty rechilus is also forbidden; such as when one knows that A did something to B leading to a controversy, the controversy quieted, and one now casually mentions the old story to B as if one does not know that A and B were involved and revives the fight.

Hilchos Rechilus, chapter 1, section 11

Furthermore, rechilus is also through writing and applies not even if one says to B that A denigrated B, but also if says he denigrated B's merchandise (as regarding lashon hara earlier, volume 1, 1:8 and 5:7), for this too engenders hatred.