A Du’a called Sayyidul Istighfar- The Best way of asking Allah for forgiveness:
اللَّهُمَّ أَنْتَ رَبِّي لّا إِلَهَ إِلَّا أَنْت،
خَلَقْتَنِي وَأَنَا عَبْدُكَ،
وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَ مَا اسْتَطَعْت،
أَعُوذُ بِكَ مِنْ شَرِّ مَا صَنَعْت،
أَبُوءُ لَكَ بِنِعْمَتِكَ
عَلَيَّ، وَأَبُوءُ بِذَنْبِي فَاغْفِر لِي فَإِنَّهُ لَا يَغْفِرُ
الذُّنُوبَ إِلَّا أَنْتَ
Allahumma anta rabbee la ilaha illa ant, khalaqtanee wa-ana AAabduk, wa-ana AAala AAahdika wawaAAdika mas-tataAAt, aAAoothu bika min sharri ma sanaAAt, aboo-o laka biniAAmatika AAalay, wa-aboo-o bithanbee, faghfir lee fa-innahu la yaghfiruth-thunooba illa ant.
‘O Allaah, You are my Lord, none has the right to be worshipped except You, You created me and I am You 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 favour upon me and I acknowledge my sin, so forgive me, for verily none can forgive sin except You.’
The Prophet, sallallahu alayhi wa Aalihi wa sallam, added, “If somebody 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 if somebody recites it at night with firm faith in it and dies before the morning he will be from the people of Paradise.”
Ash-Shaykh Muhammad bin Saalih al-Uthaymeen mentioned it is to be recited along with the morning and evening adkhar and he mentioned it is the best of the du’aas overall when asking for forgiveness.
Some of the scholars have given this du’a so much importance to the point that some have written a whole book in explaining it.
AbdulFattaah bin Uthman