“Whoever says: ‘Subḥān Allāh wa bi-ḥamdih, Subḥānaka Allāhumma wa bi-ḥamdik, Lā ilāha illā Ant, Astaghfiruka wa atūbu ilayk’ (Glorified be Allah and praised, Glorified be You, O Allah, and praised, there is no god but You, I seek Your forgiveness and repent to You) in a gathering of remembrance, it will be like a seal upon it; and whoever says it in a gathering of idle talk, it will be an expiation for it.”

Reported by al-Nasāʾī in al-Sunan al-Kubrā (no. 10185), al-Ḥākim in al-Mustadrak (no. 1970), and al-Ṭabarānī in al-Muʿjam al-Kabīr (no. 1586), from the narration of Jubayr ibn Muṭʿim — may Allah be pleased with him.
Authenticated in Ṣaḥīḥ al-Jāmiʿ (no. 6430) and Silsilat al-Aḥādīth al-Ṣaḥīḥah (no. 81).

Brief Explanation of the Hadith

Hardly any gathering is free from idle talk, heedlessness, or speech that is not praiseworthy. Thus, the noble Prophetic guidance came to teach the Muslim a supplication to say upon leaving a gathering — one that serves as an expiation for any errors or shortcomings that may have occurred during it. This supplication includes glorifying and exalting Allah, praising Him with gratitude, affirming His oneness and absolute uniqueness without partner, followed by seeking His forgiveness — presenting means (off approach to Allah) before requests. For this reason, a great reward has been attached to these words: whoever says them in a gathering of remembrance, they serve as a seal that affirms and preserves the good therein, making it acceptable before Allah. And whoever says them in a gathering of idle talk, they serve as an expiation for the sins and transgressions committed in that gathering.
A Muslim should therefore make it a habit to say this supplication in his gatherings, for rarely does a person sit in a gathering without there being some idle talk or waste of time that brings him no benefit.
The apparent meaning of the ḥadīth is that everything that occurred in the gathering is forgiven — even backbiting and slander. However, it may be that what is intended by “forgiveness” excludes the rights of other people, as it is well-known that such rights are typically excluded from the general statements regarding forgiveness. The same applies to major sins, as they are not expiated except through sincere repentance — unless these words are accompanied by remorse and a firm resolve not to return to the sin, in which case it would constitute repentance.
The ḥadīth highlights the virtue of this supplication and encourages persistence in saying it regularly.