[As] the [above] is true, [the] one who is ingrained with this evil trait, Heaven Forbid, incessantly emptying the arrows of his tongue upon his fellow, will not benefit from any wisdom or advice, even if he were to accustom himself to always [be involved] with Torah and mitzvos. [This is true], for immediately [after earning] the eternal reward from a week or two of learning Torah and performing mitzvos, [he] will [attack] his fellow with the arrows of his mouth, and [thereby] his merits [will transfer] [to his fellow] for eternity, [taking], in exchange, [from the] sins [of his fellow who was the target of his forbidden speech]. If subsequently he were to earn eternal reward for some months or years, he will [then happen upon] another person [and speak against him], thereby [transferring more of his eternal reward] to [his fellow], as mentioned above, [this pattern repeating itself] until the day of his death, Heaven Forbid. In summary: This person is likely to leave this world cleaned of his possessions, they being the eternal possessions of Torah and mitzvos [he performed]. In exchange for [the merits that he lost, he] will be full of many great, abundant, and immense sins, of various types, from [the] people [that he slandered. The slanderer will bear each of the victims’ sins] in accordance to the degree of shame and disgrace that [he caused] these [people] in his lifetime [through his forbidden speech]. Therefore, Dovid HaMelech, Alav HaShalom, warned us [that we must] first guard [our] tongue from evil, and afterwards “remove [ourselves] from evil and perform [that which is] good”, for by guarding one’s tongue, a great deal of [reward] that The Holy One, Blessed is He, sets aside for him, whether [the reward earned] is small or great, will in any case remain in his possession, and he will [thereby] not give [away] his wealth [that awaits him in The World to Come], to others.
 “Gaon” often refers to a great sage.
 This teaching is found in The Pillar of Fear page 1, third column of the Vilna printing.
 This teaching is found in “Duties of the Heart” - “Chovos HaLevavos”: Gate of Submission, chapter 7.