The Prophet Muhammad, blessings and peace be upon him, entrusted this supplication to his wife Aisha (from Jami' at-Timirdhi [hadith compilation]).
"O Allah, You are the One who forgives, You love forgiveness, so please forgive me."
Also translated as, "O Allah, You are the One who pardons, You love pardoning, so please pardon me."
Transliteration of the Arabic: Allahumma 'innaka afuwwun tuhibbul 'afwa fa'fu 'anni
— Habib Todd Boerger