Chafetz Chaim, Part Two, The Prohibition Against Rechilut, Principle 2
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אָסוּר לְסַפֵּר רְכִילוּת, אֲפִלּוּ בִּפְנֵי יָחִיד, (א) וְכָל שֶׁכֵּן בִּפְנֵי רַבִּים.
Chofetz Chaim, Silverstein translation
It is forbidden to speak rechiluth, even in the presence of one; how much more so, in the presence of many.