And if the speaker exhorted [the hearers] not to reveal it, even if he said it before many, the issur of lashon hara obtains for the one who reveals it afterwards, even by chance. And even if he sees that one of the hearers or two did not heed this exhortation and revealed [what "he" heard] to others, in spite of this, this third one, may not reveal the thing to others, even by chance. [See Be'er Mayim Chayim.]
וְאִם הָאוֹמֵר הִזְהִיר שֶׁלֹּא לְגַלּוֹתוֹ, אֲפִלּוּ אָמַר (טו) בִּפְנֵי רבִּים, יֵשׁ בּוֹ מִשּׁוּם לָשׁוֹן הָרָע, לְמִי שֶׁיְּגַלֶּה אַחַר כָּךְ אֲפִלּוּ בְּמִקְרֶה. וַאֲפִלּוּ אִם הוּא רוֹאֶה שֶׁאֶחָד מֵהשּׁוֹמְעִים אוֹ שְׁנַיִם לֹא שָׁמְרוּ אֶת הָאַזְהָרָה הַזּוֹ וְגִלּוּהוּ לַאֲחֵרִים, אַף עַל פִּי כֵן (טז) הַשְּׁלִישִׁי הַזֶּה אֵין לוֹ לְגַלּוֹת אֶת הַדָּבָר לַאֲחֵרִים אֲפִלּוּ בְּמִקְרֶה, וְעַיֵּן בִּבְאֵר מַיִם חַיִּים.
And if the speaker exhorted [the hearers] not to reveal it, even if he said it before many, the issur of lashon hara obtains for the one who reveals it afterwards, even by chance. And even if he sees that one of the hearers or two did not heed this exhortation and revealed [what "he" heard] to others, in spite of this, this third one, may not reveal the thing to others, even by chance. [See Be'er Mayim Chayim.]