Sahih Muslim 2758 a
Abu Huraira reported from Allah's Messenger (ﷺ) 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. O 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".
حَدَّثَنِي عَبْدُ الأَعْلَى بْنُ حَمَّادٍ، حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ،
 بْنِ أَبِي طَلْحَةَ عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِي عَمْرَةَ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه
 وسلم فِيمَا يَحْكِي عَنْ رَبِّهِ عَزَّ وَجَلَّ قَالَ ‏"‏ أَذْنَبَ عَبْدٌ ذَنْبًا فَقَالَ اللَّهُمَّ اغْفِرْ لِي ذَنْبِي ‏.‏
 فَقَالَ تَبَارَكَ وَتَعَالَى أَذْنَبَ عَبْدِي ذَنْبًا فَعَلِمَ أَنَّ لَهُ رَبًّا يَغْفِرُ الذَّنْبَ وَيَأْخُذُ بِالذَّنْبِ ‏.‏ ثُمَّ
 عَادَ فَأَذْنَبَ فَقَالَ أَىْ رَبِّ اغْفِرْ لِي ذَنْبِي ‏.‏ فَقَالَ تَبَارَكَ وَتَعَالَى عَبْدِي أَذْنَبَ ذَنْبًا فَعَلِمَ
 أَنَّ لَهُ رَبًّا يَغْفِرُ الذَّنْبَ وَيَأْخُذُ بِالذَّنْبِ ‏.‏ ثُمَّ عَادَ فَأَذْنَبَ فَقَالَ أَىْ رَبِّ اغْفِرْ لِي ذَنْبِي ‏.‏ فَقَالَ
 تَبَارَكَ وَتَعَالَى أَذْنَبَ عَبْدِي ذَنْبًا فَعَلِمَ أَنَّ لَهُ رَبًّا يَغْفِرُ الذَّنْبَ وَيَأْخُذُ بِالذَّنْبِ وَاعْمَلْ مَا
 شِئْتَ فَقَدْ غَفَرْتُ لَكَ ‏"‏ ‏.‏ قَالَ عَبْدُ الأَعْلَى لاَ أَدْرِي أَقَالَ فِي الثَّالِثَةِ أَوِ الرَّابِعَةِ ‏"‏ اعْمَلْ
 مَا شِئْتَ ‏"‏ ‏.‏