Chafetz Chaim, Part One, The Prohibition Against Lashon Hara, Principle 1
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הַלָּאו זֶה שֶׁכָּתַבְנוּ הוּא מַה שֶּׁכְּתַבְתּוֹ הַתּוֹרָה בְּפֵרוּשׁ מְיֻחָד לְאִסוּר זֶה שֶׁל לָשׁוֹן הָרָע וּרְכִילוּת, אֲבָל בְּלָאו הָכִי {בלא זה} יֵשׁ עוֹד הַרְבֵּה לָאוִין וַעֲשִׂין אֲחֵרִים, שֶׁהוּא עוֹבֵר עֲלֵיהֶן עַל יְדֵי סִפּוּר הָרַע הַזֶּה, כַּמְבֹאָר לְעֵיל בַּפְּתִיחָה הַקּוֹדֶמֶת, עַיֵּן שָׁם.
This negative commandment which we adduced is what the Torah stated explicitly for this issur of lashon hara and rechiluth. But aside from this, there are many other negative and positive commandments that one transgresses by speaking lashon hara, as explained above in the preceding introduction.