The Book Pertaining to Repentance and Exhortation to Repentance (Kitab Al-Tauba)
Muslim :: Book 37 : Hadith 6642
Abu Huraira reported from Allah's Messenger (may peace be upon him) that his Lord, the Exalted and Glorious, thus said. A servant committed a sin and he said: O Allah, forgive me my sins, and Allah (the Exalted and Glorious) said: My servant commited a sin and then he came to realise that he has a Lord Who forgives the sins and takes to account (the sinner) for the sin. He then again committed a sin and said: My Lord, forgive me my sin, and Allah, the Exalted and High, said: My servant committed a sin and then came to realise that he has a Lord Who would forgive his sin or would take (him) to account for the sin. He again committed a sin and said: My Lord, forgive me for my sin, and Allah (the Exalted and High) said: My servant sas committed a sin and then came to realise that he has a Lord Who forgives the sins or takes (him) to account for sin. 0 servant, do what you like. I have granted you forgiveness.
'Abd al-A'la said: I do not know whether he said thrice or four times to do" what you desire". The hadlth has been narrated on the authority of 'Abd al-A'la b. Hammad with the same chain of transmitters.