'Aishah (May Allah be pleased with her) reported:
I asked: "O Messenger of Allah! If I realize Lailat-ul-Qadr (Night of Decree), what should I supplicate in it?" He (ﷺ) replied, "You should supplicate: Allahumma innaka 'afuwwun, tuhibbul-'afwa, fa'fu 'anni (O Allah, You are Most Forgiving, and You love forgiveness; so forgive me)."[At-Tirmidhi].
App reference: Book 9, Hadith 205
Arabic/English book reference: Book 9, Hadith 1195