Sahih Muslim
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)
Book Number: 035 / Hadith Number: 6533
Abu Bakr reported that he said to Allah's Messenger (may peace be upon him): 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." This hadith has been transmitted on the authority of 'Amr b. al-'As that Abu Bakr Siddiq said to Allah's Messenger (may peace be upon him): Allah's Messenger. teach me a supplication which I should make in my prayer and in my house. The rest of the hadith is the same except with this variation that he said: Much wrong (Zulman Kathira).