Sayyid al-Istighfar (Master of Seeking Forgiveness)
The most comprehensive dua for seeking Allah's forgiveness
اَللّٰهُمَّ أَنْتَ رَبِّي لَا إِلَٰهَ إِلَّا أَنْتَ خَلَقْتَنِي وَأَنَا عَبْدُكَ وَأَنَا عَلَىٰ عَهْدِكَ وَوَعْدِكَ مَا اسْتَطَعْتُ أَعُوذُ بِكَ مِن شَرِّ مَا صَنَعْتُ أَبُوءُ لَكَ بِنِعْمَتِكَ عَلَيَّ وَأَبُوءُ لَكَ 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 bini'matika 'alayya, wa abu'u laka bidhanbi faghfir li fa innahu la yaghfirudh-dhunuba illa anta.
O Allah, You are my Lord, none has the right to be worshipped except You, You created me and I am Your servant and I abide to Your covenant and promise as best I can, I take refuge in You from the evil of which I committed. I acknowledge Your favor upon me and I acknowledge my sin, so forgive me, for verily none can forgive sin except You.