Sunan At-Tirmidhi

Ibn Umar said:“In one sitting of the Messenger of Allah (ﷺ), one could count that he said a hundred time, before he would get up: ‘O my Lord, forgive me, and accept my repentance. Verily, You are the Oft-Returning, the Most Forgiving (Rabbighfirlī watub `alayya innaka antat-Tawwābul-Ghafūr).’”