Dua On Lailatul Qadr - the Night of Power in the month of Ramadan

Aishah (radhiya Allahu Ta'ala anha), that she said:
"O Messenger of Allah! What if I knew which night Lailatul-Qadr was, then what should I say in it?"
He said 'Say

اَللَّهُمَّ اِنَّكَ عَفُوٌّ ، تُحِبُّ الْعَفْوَ فَاعْفُ عَنِّي

Allahumma innaka 'affuwwun tuhibbul 'afwa fa'fu 'anni' "

O Allah You are The One Who pardons greatly, and loves to pardon, so pardon me.
[at Tirmidhi]