Narrated Abdullah ibn Umar (RA): We counted that the Messenger of Allah (ﷺ) would say this dua a hundred times during a meeting -

رَبِّ اغْفِرْ لِي وَتُبْ عَلَيَّ إِنَّكَ أَنْتَ التَّوَّابُ الرَّحِيمُ (الْغَفُوْرُ)

Rabbighfirli Watub Alayya Innaka Antat-Tawwabul- rahim [in another narration there is al-Ghaffur instead of al-Rahim]

Lord, forgive me and repent for me, for you are The Most Merciful The Acceptor of Repentance. In another narration there is "The Forgiver" instead of "The Acceptor of Repentance"

Reference: Sahih. Abu Dawud: 1516