Shaddad bin Aus (RAA) narrated that the Messenger of Allah (ﷺ) said:

“The best manner of asking for forgiveness is to say: “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 by your covenant and promise as best I can. I seek refuge in you from the evil, which I have committed. I acknowledge your favor upon me and I knowledge my sins, so forgive me, for verily none can forgive sin except you.” Related by Al-Bukhari.

وَعَنْ شَدَّادِ بْنِ أَوْسٍ ‏- رضى الله عنه ‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ سَيِّدُ اَلِاسْتِغْفَارِ, أَنْ يَقُولَ اَلْعَبْدُ: اَللَّهُمَّ أَنْتَ رَبِّي, لَا إِلَهَ إِلَّا أَنْتَ, خَلَقْتَنِي, وَأَنَا عَبْدُكَ, وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَ مَا اِسْتَطَعْتُ, أَعُوذُ بِكَ مِنْ شَرِّ مَا صَنَعْتُ, أَبُوءُ لَكَ بِنِعْمَتِكَ عَلَيَّ, وَأَبُوءُ لَكَ بِذَنْبِي, فَاغْفِرْ لِي; فَإِنَّهُ لَا يَغْفِرُ اَلذُّنُوبَ إِلَّا أَنْتَ } أَخْرَجَهُ اَلْبُخَارِيُّ .‏ [1]‏ .‏