A'ishah (radhiallahu `anha) reported that she asked Allah's Messenger (sallallahu `alayhi wa sallam),
"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: "Allahumma innaka `afuwwun tuh.ibbul `afwa fa`fu `annee - O Allah! You are forgiving, and you love forgiveness. So forgive me." Recorded by Ahmad, Ibn Majah, and at-Tirmithi. Verified to be authentic by Al-Albani
