ENOfficial
‘A'isha said she asked God’s messenger to tell her what prayers to say on lailat al-qadr if she knew which night it was, and he told her to say, “O God, Thou art forgiving and lovest forgiveness, so forgive me.” Ahmad, Ibn Majah, and Tirmidhi transmitted it, and Tirmidhi declared it to be sound.
Source: sunnah.com
Other translations
Arabic
وَعَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ: قُلْتُ: يَا رَسُولَ اللَّهِ أَرَأَيْتَ إِنْ عَلِمْتُ أَيُّ لَيْلَةٍ الْقَدْرِ مَا أَقُولُ فِيهَا؟ قَالَ: " قُولِي: اللَّهُمَّ إِنَّكَ عَفُوٌّ تُحِبُّ الْعَفْوَ فَاعَفُ عَنِّي ". رَوَاهُ أَحْمد وَابْن مَاجَه وَالتِّرْمِذِيّ وَصَححهُ
sunnah.com