Chafetz Chaim, Part Two, The Prohibition Against Rechilut, Principle 6
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דִּין אִסוּר קַבָּלַת רְכִילוּת (יז) הוּא אֲפִלּוּ מִמֵּסִיחַ לְפִי תֻּמּוֹ, דְּהַיְנוּ שֶׁהוּא רוֹאֶה שֶׁהַמְסַפֵּר לֹא כִּוֵּן בָּזֶה לְעוֹרֵר מְדָנִים עַל חֲבֵרוֹ, רַק שֶׁבְּמִקְרֶה יָצָא דָּבָר זֶה מִפִּיו. וְכָל יֶתֶר פְּרָטָיו מְבֹאָר לְעֵיל בְּחֵלֶק א' בִּכְלָל ז' בְּסָעִיף ט' לְעִנְיַן לָשׁוֹן הָרָע, וְהוּא הַדִּין לְעִנְיַן רְכִילוּת.
The din of the issur of accepting rechiluth obtains even when he speaks 'in his innocence." That is, when he [the hearer] sees that the speaker did not intend to stir up strife against his friend, but that it [the rechiluth] left his mouth by chance. (All of its other details are explained above in Part One, Principle VII, section 9, in respect to lashon hara. The same applies to rechiluth.)