حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا لَيْثٌ، ح وَحَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَخْبَرَنَا اللَّيْثُ، عَنْ يَزِيدَ بْنِ أَبِي حَبِيبٍ، عَنْ أَبِي الْخَيْرِ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو، عَنْ أَبِي بَكْرٍ، أَنَّهُ قَالَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم عَلِّمْنِي دُعَاءً أَدْعُو بِهِ فِي صَلاَتِي قَالَ ‏"‏ قُلِ اللَّهُمَّ إِنِّي ظَلَمْتُ نَفْسِي ظُلْمًا كَبِيرًا - وَقَالَ قُتَيْبَةُ كَثِيرًا - وَلاَ يَغْفِرُ الذُّنُوبَ إِلاَّ أَنْتَ فَاغْفِرْ لِي مَغْفِرَةً مِنْ عِنْدِكَ وَارْحَمْنِي إِنَّكَ أَنْتَ الْغَفُورُ الرَّحِيمُ ‏"‏ ‏.‏

Abu Bakr reported that he said to Allah's Messenger (PBUH): Teach me a supplication which I should recite in my prayer. Thereupon he (the Holy Prophet) said: Recite:" O Allah, I have done great wrong to myself." According to Qutaiba (the words were: ) much (wrong) -there is none to forgive the sins but Thou only, say:" Grant me pardon from Thyself, have mercy upon me for Thou art much Forgiving and Compassionate." Translation Not Available

Book Ref: Sahih Muslim Book 48 Hadith 6533
Web Ref:  Sahih Muslim Book 35 Hadith 2705 a