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 عَلَىَّ إِنَّكَ أَنْتَ التَّوَّابُ الرَّحِيْمُ

Rabbighfirli wa tub `alayya innaka Antat-Tawwabur-Rahim

O Allah forgive me and accept my repentance, for You are the Accepter of repentance, the Most Merciful.

Reference: Sahih (Albani). Abu Dawud: 1516