Sayyid al-Istighfar
Said onceاللَّهُمَّ أَنْتَ رَبِّي لَا إِلَهَ إِلَّا أَنْتَ، خَلَقْتَنِي وَأَنَا عَبْدُكَ، وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَ مَا اسْتَطَعْتُ، أَعُوذُ بِكَ مِنْ شَرِّ مَا صَنَعْتُ، أَبُوءُ لَكَ بِنِعْمَتِكَ عَلَيَّ، وَأَبُوءُ بِذَنْبِي فَاغْفِرْ لِي فَإِنَّهُ لَا يَغْفِرُ الذُّنُوبَ إِلَّا أَنْتَ
Allahumma anta Rabbi la ilaha illa anta, khalaqtani wa ana 'abduka, wa ana 'ala 'ahdika wa wa'dika mastata'tu. A'udhu bika min sharri ma sana'tu. Abu'u laka bi ni'matika 'alayya, wa abu'u bi dhanbi, faghfir li fa innahu la yaghfirudh-dhunuba illa anta
O Allah, You are my Lord, there is no deity except You. You created me and I am Your servant. I abide by Your covenant and Your promise as best I can. I seek refuge in You from the evil of what I have done. I acknowledge Your favour upon me and I acknowledge my sin, so forgive me, for none forgives sins except You.
Hisnul Muslim 79, Bukhari 6306 · Hadith
The master supplication for forgiveness. Whoever says it with conviction in the day and dies that evening enters Paradise.