Allāhumma ‘innī ẓalamtu nafsī ẓulman kathīran, wa lā yaghfiru-dhdhunūba illā 'anta, faghfir lī maghfiratam’min `indika warḥamnī innaka 'anta ‘l-Ghafūr ur-Rahīm. O Allah, I have greatly wronged myself, and no one forgives sins but You. So, grant me forgiveness and have mercy on me. Surely, you are Forgiving, Merciful. Reference: Al-Bukhari 8/168, Muslim 4/2078.

اللّهُـمَّ إِنِّـي ظَلَـمْتُ نَفْسـي ظُلْمـاً كَثـيراً وَلا يَغْـفِرُ الذُّنـوبَ إِلاّ أَنْت، فَاغْـفِر لي مَغْـفِرَةً مِنْ عِنْـدِك وَارْحَمْـني، إِنَّكَ أَنْتَ الغَـفورُ الرَّحـيم