Hadith 4857
Narrated Abdullah ibn Amr ibn al-As: There are some expressions which a man utters three times when he gets up from an assembly he will be forgiven for what happened in the assembly; and no one utters them in an assembly held for a noble cause or for remembrance of Allah but that is stamped with them just as a document is stamped with a signet-ring. These expressions are: Glory be to Thee, O Allah, and I begin with praise of Thee, there is no god but thou; I ask Thy pardon, and return to Thee in repentance.
Hadith 4858
A similar tradition has also been transmitted by Abu Hurairah from the Prophet ﷺ through a different chain of narrators.
Hadith 4859
Narrated Abu Barzah al-Aslami: When the Messenger of Allah ﷺ intended to get up from the assembly he used to say in the last. Glory be to Thee. O Allah, and I begin with praise of Thee, I testify that there is no god but Thou; I ask Thy pardon, and return to Thee in repentance. The man asked: Messenger of Allah! you utter the words now which you did not do in the past? He replied: (This is an) atonement for what takes place in the assembly.