In one narration the wording is: "The expiation of a gathering is that a person, before getting up, recites these words: 'Subhanaka Allahumma wa bihamdika, la ilaha illa anta, tub 'alayya waghfir li' (You are free of every imperfection, O Allah, and praise belongs to You; there is no god but You; accept my repentance and forgive me). He should recite these words three times. If it is a gathering of idle talk, these (words) will become an expiation for him, and if it is a gathering of remembrance, these (words) will become a seal upon it." Imam al-Tabarani recorded all of these narrations, and the narrators of the first narration are the narrators of the Sahih. (Allamah al-Haythami says:) I say: The various chains of this hadith have already passed in "Kitab al-Adhkar".
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب أهل الجنة / 18776