رَبَّنَا ظَلَمْنَا أَنفُسَنَا وَإِن لَّمْ تَغْفِرْ لَنَا وَتَرْحَمْنَا لَنَكُونَنَّ مِنَ الْخَاسِرِينَ
Rabbanaa zalamnaa afusanaa wa in lam taghfir lanaa wa tarhamnaa lanakuunanna minal-khaasiriin. (7:23)
Our Lord, we have wronged our souls. And if You do not forgive us and grant us mercy, we shall certainly be among the losers.
Ameen
This du’aa was taught by Allah Ta’aala to Sayyidnaa Adam (a.s.). The Qur’aan says: “Then Adam learned certain words (of du’aa) from his Lord; so Allah accepted his repentance” (Al-Baqarah, 2:37).
(Source: Khalid Baig’s commentary to du’aa #10 in the Accepted Whispers: Munajat-e-Maqbul)