Sunan at-Tirmithiy كتاب الدعوات باب ما يقول إذا قام من المجلس
It was observed that the Messenger of God, peace and blessings of God be upon him, [supplicated] in [any] gathering, "O my Lord, forgive me and accept my repentance. Verily, You are The Acceptor of repentance, The Ever-Forgiving," a hundred times, before he left. Click on ḥadīth to read more