Chafetz Chaim, Part One, The Prohibition Against Lashon Hara, Principle 7
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וְדַע, דַּאֲפִלּוּ דְּבָרִים הַנִּכָּרִים מַמָּשׁ, אֵינוֹ מוֹעִיל רַק לְעִנְיַן, שֶׁעַל יְדֵי זֶה יִהְיֶה מֻתָּר לְהַאֲמִין בְּעַצְּמוֹ אֶת הַדָּבָר שֶׁמְּסַפְּרִין לוֹ, אֲבָל לְעִנְיַן לֵילֵךְ אַחַר כָּךְ וּלְסַפֵּר דָּבָר זֶה לַאֲחֵרִים, לֹא מְהַנֵּי {לא מועיל}, דְּלֹא עָדִיף, מֵאִם רָאָה בְּעַצְמוֹ דְּבַר גְּנוּת עַל חֲבֵרוֹ, (כח) שֶׁאָסוּר לְסַפֵּר אַחַר כָּךְ לַאֲנָשִׁים, וּכְמוֹ שֶׁמְּבֹאָר לְעֵיל בִּכְלָל ד' סָעִיף ג' וְד'. וְדַע עוֹד (כט) דִּבְכָל אֹפֶן אָסוּר לִסְמֹךְ עַל הֶתֵּר זֶה שֶׁל דְּבָרִים הנִּכָּרִים מַמָּשׁ (ל) לְהַפְסִידוֹ עַל יְדֵי זֶה בְּמָמוֹן (לא) אוֹ לְהַכּוֹתוֹ.
And know that even with "real indications," this is of avail only as far as being permitted to believe himself the thing that is told him, but as far as going afterwards and telling it to others, it is of no avail. For it has no advantage over he himself seeing something demeaning in his friend, in which instance he is forbidden afterwards to tell others, as explained above in Principle IV, section IV. And know further that in any case it is forbidden to rely upon this heter of "real indications" to cause him monetary loss thereby or to strike him.