Jami at-Tirmidhi 3433 (sahih, al-Albani)

قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ مَنْ جَلَسَ فِي مَجْلِسٍ فَكَثُرَ فِيهِ لَغَطُهُ فَقَالَ قَبْلَ أَنْ يَقُومَ مِنْ مَجْلِسِهِ ذَلِكَ سُبْحَانَكَ اللَّهُمَّ وَبِحَمْدِكَ أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ أَنْتَ أَسْتَغْفِرُكَ وَأَتُوبُ إِلَيْكَ ‏.‏ إِلاَّ غُفِرَ لَهُ مَا كَانَ فِي مَجْلِسِهِ ذَلِكَ ‏"‏ ‏.‏

“Abu Hurairah narrated that:The Messenger of Allah ﷺ said: “Whoever sits in a sitting and engages in much empty, meaningless speech and then says before getting from that sitting of his: ‘Glory is to You, O Allah, and praise, I bear witness that there is none worthy of worship except You, I seek You forgiveness, and I repent to You, (Subḥānaka Allāhumma wa biḥamdika, ashhadu an lā ilāha illā anta, astaghfiruka wa atūbu ilaik)’ whatever occurred in that sitting would be forgiven to him.””