رَبَّنَا ظَلَمْنَا أَنْفُسَنَا وَإِنْ لَمْ تَغْفِرْ لَنَا وَتَرْحَمْنَا لَنَكُونَنَّ مِنَ الْخَاسِرِينَ
Transliteration
Rabbana zalamna anfusana wa in lam taghfir lana wa tarhamna lanakunanna minal-khasirin
English meaning
Our Lord, we have wronged ourselves, and if You do not forgive us and have mercy upon us, we will surely be among the losers.
When is it recited?
Recited during repentance.
Its virtue
The first supplication of Adam (AS) and Hawwa when repenting.
Source
Al-A'raf 7:23