Eruvin 64b: Anyone who vows is proper to be pierced with a sword, but the words of Chachamim heal. I.e., they can permit his vow.

Rashi: Boteh is speaking, like "Levatei bi'Sefasayim" (Vayikra 5:4). His words cause people to feud and murder. Chachamim's Lashon brings Shalom Bein Adam l'Chavero, and heal his words.

R. Yonah: Some pain their colleagues verbally, with words of pride and scorn that touch the Nefesh and make the face blush. Or, he tells Leshon ha'Ra, and the listeners rely on his words. One who maligns [lineage of] a family never gets atonement ¹ . Chachamim cure the damage via Leshon ha'Ra - they prevent him [from repeating it], rebuke him and nullify his words, and inform [people] of the punishment for accepting Leshon ha'Ra.

Malbim: The liar is Boteh (vows and swears) to support his words. It is like piercing with a sword - it stabs his opponent and unjustly forces him to pay. Chachamim's words are a cure for this stabbing. Lashon is speech in the way of Binah. Chachamim who conduct according to the laws of Chachmah, they investigate with Lashon in the way of Binah and proofs, to understand a matter amidst a matter, recognize the scheme and heal the stabbed victim.