رَبَّنَا ظَلَمْنَا أَنْفُسَنَا وَإِنْ لَمْ تَغْفِرْ لَنَا وَتَرْحَمْنَا لَنَكُونَنَّ مِنَ الْخَاسِرِينَ
Rabbana zalamna anfusana wa in lam taghfir lana wa tarhamna lanakuanna minal-khasirin
Our Lord, we have wronged ourselves. If You do not forgive us and have mercy on us, we will surely be among the losers.
Recite when seeking forgiveness for sins and mistakes
This was the first dua of repentance taught to humanity. Adam and Hawwa (Eve) said this after their sin, and Allah accepted their repentance.