Chazal have said: For three transgressions punishment is exacted of a man in this world, and he has no share in the world to come: idolatry, illicit relations, and blood-spilling — and lashon hara over and above all. Chazal have proved this from Scripture. And the Rishonim have explained that the reference is to those who are habituated to this sin [lashon hara] and who do not take it upon themselves to guard themselves against it, the thing having become "permitted" to them.
אָמְרוּ חֲזַ"ל: עַל שָׁלש עֲבֵרוֹת נִפְרָעִין מִן הָאָדָם בָּעוֹלָם הַזֶּה, וְאֵין לוֹ חֵלֶק לָעוֹלָם הַבָּא, וְאֵלּוּ הֵן: עֲבוֹדָה זָרָה וְגִלּוּי עֲרָיוֹת וּשְׁפִיכוּת דָּמִים, וְלָשׁוֹן הָרָע נֶגֶד כֻּלָּן. וְהֵבִיאוּ חֲזַ"ל עַל זֶה רְאָיָה מִן הַכְּתוּבִים, וּפֵרְשׁוּ הָרִאשׁוֹנִים, דְּהַכַּוָּנָה עַל אֵלּוּ שֶׁהֻרְגְּלוּ בּעוֹן זֶה בִּתְמִידוּת, וְאֵין מְּקבְּלִים עַל עַצְּמָם לְהִשָּׁמֵר מִּמֶּנּוּ, מִפְּנֵי שֶׁנַּעֲשָׂה הדָּבָר אֶצְּלָם כְּהֶתֵּר.
Chazal have said: For three transgressions punishment is exacted of a man in this world, and he has no share in the world to come: idolatry, illicit relations, and blood-spilling — and lashon hara over and above all. Chazal have proved this from Scripture. And the Rishonim have explained that the reference is to those who are habituated to this sin [lashon hara] and who do not take it upon themselves to guard themselves against it, the thing having become "permitted" to them.