Hilchos Rechilus, chapter 4, section 2 3

If Reuven denigrated Shimon in front of two people, and one of them informed Shimon,
the second should still not speak of the episode to Shimon. This applies not even when Shimon
is unsure whether the story is true, for example, if he asked the second person if Reuven really
denigrated him, but even generally. Because repeating the story increases Shimon’s hate for
To repent the sin of rechilus, one must appease the person spoken of, regret what one did,
confess the sin, and accept upon oneself wholeheartedly not to do it again. If one clearly knows
that no harm was caused by the rechilus, one does not need to appease the person spoken of.