Sahih Muslim 6869
صحيح مسلم#6869SahihAbu Bakr reported that he said to Allah's Messenger (ﷺ):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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 48:63