Chafetz Chaim, Part Two, The Prohibition Against Rechilut, Principle 1
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וְדַע עוֹד, דְּאֵין חִלּוּק בְּאִסוּר רְכִילוּת, בֵּין אִם הוּא מְסַפֵּר לוֹ בְּפֵרוּשׁ, מַה שֶּׁאֶחָד עָשָׂה לוֹ, אוֹ דִּבֵּר עָלָיו, וּבֵין עַל יְדֵי (כ) מִכְתָּב. וְאַחַת הִיא, אִם הוּא מְסַפֵּר לוֹ, שֶׁפְּלוֹנִי גִּנָּה אוֹתוֹ בְּעַצְמוֹ, אוֹ שֶׁמְּסַפֵּר לוֹ שֶׁפְּלוֹנִי גִּנָּה אֶת סְחוֹרָתוֹ, (כְּמוֹ לעִנְין לָשׁוֹן הָרָע בְּחֵלֶק א' כְּלָל א' סָעִיף ח' וּכְלָל ה' סָעִיף ז') כֵּיוָן שֶׁעַל יְדֵי זֶה מַכְנִיס שִׂנְאָה בְּלִבּוֹ עָלָיו.
And know further that there is no difference in the issur of rechiluth as to whether he states explicitly what someone did to him or said about him, or whether he puts it into writing. And it is the same whether he tells him that someone has demeaned him personally or that he has demeaned his wares, since through this [(all of the modes)] he injects hatred into his heart against him.