(כא) מָ֣וֶת וְ֭חַיִּים בְּיַד־לָשׁ֑וֹן וְ֝אֹהֲבֶ֗יהָ יֹאכַ֥ל פִּרְיָֽהּ׃
(21) Death and life are in the power of the tongue; Those who love it will eat its fruit.
(16) Do not go about as a talebearer among your fellows. Do not stand by the blood of your neighbour: I am the Eternal.
רַמְבַּ"ם, מִשְׁנֵה תוֹרָה, הִלְכוֹת דֵּעוֹת פֶּרֶק ז הֲלָכָה ב
אֵי זֶהוּ רָכִיל זֶה שֶׁטוֹעֵן דְּבָרִים וְהוֹלֵךְ מִזֶּה לָזֶה וְאוֹמֵר כָּךְ אָמַר פְּלוֹנִי כָּךְ וְכָךְ שָׁמַעְתִּי עַל פְּלוֹנִי אַעַ"פִּ שֶׁהוּא אֱמֶת הֲרֵי זֶה מַחֲרִיב אֶת הָעוֹלָם, יֵשׁ עָוֹן גָּדוֹל מִזֶּה עַד מְאֹד וְהוּא בִכְלַל לָאו זֶה וְהוּא לְשׁוֹן הָרָע, וְהוּא הַמְּסַפֵּר בִּגְנוּת חֲבֵירוֹ אַעַ"פִּ שֶׁאוֹמֵר אֱמֶת, אֲבָל הָאוֹמֵר שֶׁקֶר נִקְרָא מוֹצִיא שֵׁם רָע עַל
חֲבֵירוֹ, אֲבָל בַּעַל לְשׁוֹן הָרָע זֶה שֶׁיוֹשֵׁב וְאוֹמֵר כָּךְ וְכָךְ עָשָׂה פְלוֹנִי וְכָךְ וְכָךְ הָיוּ אֲבוֹתָיו וְכָךְ וְכָךְ שָׁמַעְתִּי עָלָיו וְאָמַר דְּבָרִים שֶׁל גְּנַאי, עַל זֶה אָמַר הַכָּתוּב יַכְרֵת ה' כָּל שִׂפְתֵי חֲלָקוֹת לָשׁוֹן מְדַבֶּרֶת גְּדוֹלוֹת (תהלים יב, ד)
Rambam, Mishneh Torah, Hilkhot Deot 7:2
Who is a rakhil [ רָכִיל ] (talebearer)? One who carries gossip, going from person to person and saying: “So and so said this; this is what I heard about so and so.” Even though it is the truth, they ruin the world.
There is still a worse sin that is included in this prohibition, namely: lashon hara [ לָשׁוֹן הָרָע ]. And that is: One who says bad things about their neighbour, even if they are telling the truth.
But someone who lies is called a motzi shem ra [ מוֹצִיא שֵׁם רָע ] (a slanderer).
A “ba’al lashon hara” [ בַּעַל לָשׁוֹן הָרָע ] (master of the evil tongue) is one who
sits and says: “this is what so and so did, such were his ancestors, this is what I have heard about them” saying bad things. About this scripture says:
“May God cut off all flattering lips, the tongue that speaks proud things!” (Psalms 12:4)