`A’ishah (radhiallahu `anha) reported that she asked Allah’s Messenger (pbuh), “O Messenger of Allah! If I knew which night is Laylat ul-Qadr, what should I say during it?” And he instructed her to say:

اللْهُمَّ إِنَّكَ عَفُوٌّ تُحِبُّ الْعَفْوَ فَاعْفُ عَنِّي

Allahumma innaka `afuwwun tuh.ibbul `afwa fa`fu `annee 

“ O Allah! Verily You are the Oft-Pardoning,You love to pardon,so pardon me..”