The master dua of istighfar (Sayyid al-Istighfar)
from the Prophet ﷺ: "The master of seeking forgiveness from Allah is:
"allāhuma anta rabbī lā ilāha illā anta, khalaqtanī wa-ana ʿabduka, wa-ana ʿalá ʿahdika wa-waʿdika mā istaṭaʿtu, aʿūdhu bika min shari mā ṣanaʿtu, abūʾu laka bi-niʿmatika ʿalayya wa-abūʾu laka bi-dhanbī, fa-ighfir lī, fa-innahū lā yaghfiru al-dhunūba illā anta."
(O Allah, You are my Lord; there is no deity except You. You created me, and I am Your servant, and I am on the covenant and promise to the best of my ability. I seek refuge with You from the evil of what I have done, and I acknowledge Your favor upon me, and I confess my sins. So forgive me, for surely, there is none who forgives sins except You.)
He added, "If someone says 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 Jannah; and if someone say it at night with firm faith in it, and dies before the morning, he will be from the people of Jannah."
عَنِ النَّبِيِّ ﷺ: «سَيِّدُ الاِسْتِغْفَارِ أَنْ تَقُولَ:
(اللَّهُمَّ أَنْتَ رَبِّي لاَ إِلَهَ إِلاَّ أَنْتَ، خَلَقْتَنِي وَأَنَا عَبْدُكَ، وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَ مَا اسْتَطَعْتُ؛ أَعُوذُ بِكَ مِنْ شَرِّ مَا صَنَعْتُ؛ أَبُوءُ لَكَ بِنِعْمَتِكَ عَلَىَّ، وَأَبُوءُ لَكَ بِذَنْبِي؛ فَاغْفِرْ لِي، فَإِنَّهُ لاَ يَغْفِرُ الذُّنُوبَ إِلاَّ أَنْتَ۔)»
قَالَ: «وَمَنْ قَالَهَا مِنَ النَّهَارِ مُوقِنًا بِهَا فَمَاتَ مِنْ يَوْمِهِ قَبْلَ أَنْ يُمْسِيَ فَهُوَ مِنْ أَهْلِ الْجَنَّةِ، وَمَنْ قَالَهَا مِنَ اللَّيْلِ وَهْوَ مُوقِنٌ بِهَا فَمَاتَ قَبْلَ أَنْ يُصْبِحَ فَهْوَ مِنْ أَهْلِ الْجَنَّةِ۔»