(א) לֹ֥א תִשָּׂ֖א שֵׁ֣מַע שָׁ֑וְא אַל־תָּ֤שֶׁת יָֽדְךָ֙ עִם־רָשָׁ֔ע לִהְיֹ֖ת עֵ֥ד חָמָֽס׃ (ס)
(1) You must not carry false rumors; you shall not join hands with the guilty to act as a malicious witness:
(רפא) שלא לשמוע מאחד מבעלי דינין ואין חברו עימו, שנאמר "לֹא תִשָּׂא שֵׁמַע שָׁוְא" (שמות כג, א).
(281) Not to hear one litigant except in the presence of the other. Ex. 23.1.
(רפו) שלא יעיד בעל עבירה, שנאמר "אַל תָּשֶׁת יָדְךָ עִם רָשָׁע לִהְיוֹת עֵד חָמָס" (שמות כג, א).
(286) Not to accept the testimony of a wicked person. Ex. 23.1.
Chofetz Chaim, Introduction to the Laws of the Prohibition of Lashon Hara and Rechilut, Opening Comments 7
First we must know the principles of these halachoth of lashon hara and rechiluth. ("Lashon hara" is speaking disparagingly against one's friend, and "rechiluth," telling one the evil thing that his friend has spoken against him or done against him.) [The principles]: It [lashon hara and rechiluth] is forbidden even if true, as will be explained below, please Gd, in the name of all the poskim. Also, the prohibition of lashon hara and rechiluth applies both in his [the object's] presence and not in his presence. Also, there is no difference between speaking and receiving [lashon hara and rechiluth], all of which we shall explain further. A "receiver" of lashon hara is one who believes in his heart what is told him by his friend even if he does not abet him in the telling but only believes in his heart the lashon hara and rechiluth that he has heard. If he does believe it, he is called "the bearer of a false report" and transgresses (Shemoth 23:1): "Do not bear a false report." All of these principles have roots and branches, as in the other parts of the Torah. May the Lrd grant that we know them comprehensively.
English
(ז) כת מספרי לשון הרע נחלקת לששה חלקים: האחד: מי שהוא אומר רע על בני אדם, שכן עשו לו. ולפעמים יאמר דופי על אדם כשר ונקי – אז הוא משקר וגם מספר לשון הרע. והוזהרנו מן התורה שלא לקבל לשון הרע. ודע: כאשר יודה השומע על לשון הרע – אז הוא כמו מספר, כי כל השומעים שהוא מודה יאמרו: כיון שהוא מודה, אם כן אמת הוא הדבר. ואפילו אם לא יודה אלא שומע ומראה עצמו כמקשיב אל הדברים ומאמין בדברים בפני בני אדם – בזה יאמינו גם אחרים. והוא מסייע למספר לשון הרע, כי אם היה גוער במספר לשון הרע – היה מונע עצמו מלספר לו יותר. אבל עתה שהוא מקשיב ומראה לו פנים – אז גורם לו לדבר יותר. והזהירנו במצוות לא תעשה (שמות כג א): "לא תשא שמע שווא" – שלא נאמין סיפור לשון הרע בלבבנו, להחזיק במחשבותינו שהדברים אמת, ולהבזות בעינינו את מי שנאמרו עליו.
(7) Gossips may be divided into six categories. The first is he who speaks evil of people and says, "Thus did they do," when in fact they did not do so, and at times he will slander an honorable and innocent person — in which case he is both a liar and a gossip. And we have been warned by the Torah not to accept gossip because it may be false, as it is said, "Thou shalt not utter a false report" (Ex. 23:1). And one who speaks gossip, will also be quick to accept gossip. And you should know that if one who hears gossip endorses what he has heard, then he is just as guilty as the gossiper. For all who hear that he agreed, will say, "Since he endorses it, it must be true." And even if he does not agree, but simply listens intently to the words, and appears to believe them, in the presence of people, he causes others to believe them too, and thus he helps the gossiper. For if he were to scold the gossiper, then he might restrain him from telling more, but since he pays attention and shows that he is interested, he causes him to speak even more gossip. And, behold, we have been warned by the verse, "Thou shalt not utter a false report" that we should not believe a gossip story in our hearts, for this would leave a strong imprint in our thoughts that the words are true and cause us to despise the object of the gossip.