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The Prophet (SAW) instructed his wife Aisha (RA) to say this if she knew which night was Laylatul Qadr. (Hint: it is a dua)
What is اللهم إنك عفوٌ تُوحِبُ الغَفوَ فاعفُ عَني
Allahumma innaka 'affuwwun tuhibbul 'afwa fa'fu 'anni'
O Allâh! You are forgiving, and you love forgiveness. So forgive me.