SEFER CHOFETZ CHAIM
Included in the prohibition against speaking rechilus is relating information which might ultimately cause ill will if it were to be passed on to a certain person or persons.
Therefore, it is forbidden to say anything to anyone that might cause animosity between any two people. One must assume that whatever is told to even one person is likely to be repeated to others – and could ultimately be heard by just about anybody. Only if the listener is warned not to tell anyone what he is about to hear, and can be trusted to heed this warning, would it be permitted to share such information with him (provided, of course, that the information is not of a derogatory nature; otherwise, it would be loshon hora).
SEFER SHMIRAS HALOSHON
As mentioned above, one who seeks to acquire the quality of shmiras haloshon must strengthen his bitachon, trust in Hashem, so that he will not become upset if someone will cause him any sort of hurt or loss. With proper bitachon, one will refrain from speaking negatively in such instances and will refrain, as well, from feuding with or shaming the guilty party. Rather, he will be confident that Hashem will replenish his losses in the way that He sees fit.
The Talmud states: “Whoever places his trust in the Holy One, Blessed is He, will merit that He will be a refuge for him in this world and the next” (Menachos 29b). This assurance is granted even to those whose trust is not predicated on a desire to honor G-d’s Name. Surely, then, one will merit this reward if he refrains from argument out of concern that he might utter that which the Torah prohibits. Moreover, one who refrains from “exacting his rightful measure” out of concern that Hashem’s Name not be desecrated, and instead places his trust in Him, will surely merit infinite reward.