Hadhrat Aisha(Radiallahu anha) said: I asked the Messenger of Allah: ‘O Messenger of Allah, if I know what night is the night of Qadr, what should I say during it?’ He said: ‘Say: O Allah, You are pardoning and You love to pardon, so pardon me.’(Ahmad, Ibn Majah, and Tirmidhi).

  اَللَّهُمَّ اِنَّكَ عَفُوٌّ ، تُحِبُّ الْعَفْوَ فَاعْفُ عَنِّي

Transliteration:

‘Allahumma innaka ‘afuwwun tuhibbul ‘afwa fa’fu ‘annee’.

Translation:

“O Allah, Thou art the One who grants pardon for sins. Thou lovest to pardon, so O pardon me.”