Shaddad ibn Aws (May Allah be pleased with him) relates that the Prophet (May Allah bless him and give him peace) said, “The (Sayyid al-Istighfar) most superior way of asking for forgiveness from Allah is to say (the du’a below). Whosoever recites it during the day with firm faith in it, and dies on the same day before the evening, he will be from the people of Paradise; and whosoever recites it at night with firm faith in it, and dies before the morning, he will be from the people of Paradise.”
[Sahih al-Bukhari; 8,75,318, at-Tirmidhi; 3393, an-Nasa’i; 5522, Ahmad; 16662]
اللَّهُمَّ أَنْتَ رَبِّي لا إِلَهَ إِلا أَنْتَ خَلَقْتَنِي وَأَنَا عَبْدُكَ وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَ مَا اسْتَطَعْتُ أَعُوذُ بِكَ مِنْ شَرِّ مَا صَنَعْتُ أَبُوءُ لَكَ بِنِعْمَتِكَ عَلَيَّ وَأَبُوءُ لَكَ بِذَنْبِي فَاغْفِرْ لِي فَإِنَّهُ لا يَغْفِرُ الذُّنُوبَ إِلا 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 ‘alaiya, wa Abu’u Laka bidhanbi faghfirli fainnahu la yaghfiru adhdhunuba illa anta
O Allah! You are my Lord! None has the right to be worshipped but You. You created me and I am Your slave, and I am faithful to my covenant and my promise as much as I can. I seek refuge with You from all the evil I have done. I acknowledge before You all the blessings You have bestowed upon me, and I confess to You all my sins. So I entreat You to forgive my sins, for nobody can forgive sins except You.