Sahih Muslim 2621
Jundub reported that Allah's Messenger (ﷺ) stated that a person said:
Allah would not forgive such and such (person). Thereupon Allah the Exalted and Glorious, said: Who is he who adjures about Me that I would not grant pardon to so and so; I have granted pardon to so and so and blotted out his deeds (who took an oath that I would not grant pardon to him).
حَدَّثَنَا سُوَيْدُ بْنُ سَعِيدٍ، عَنْ مُعْتَمِرِ بْنِ سُلَيْمَانَ، عَنْ أَبِيهِ، حَدَّثَنَا أَبُو عِمْرَانَ الْجَوْنِيُّ،
 عَنْ جُنْدَبٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم حَدَّثَ ‏
"‏ أَنَّ رَجُلاً قَالَ وَاللَّهِ لاَ يَغْفِرُ اللَّهُ
 لِفُلاَنٍ وَإِنَّ اللَّهَ تَعَالَى قَالَ مَنْ ذَا الَّذِي يَتَأَلَّى عَلَىَّ أَنْ لاَ أَغْفِرَ لِفُلاَنٍ فَإِنِّي قَدْ غَفَرْتُ لِفُلاَنٍ
 وَأَحْبَطْتُ عَمَلَكَ ‏"‏ ‏.‏ أَوْ كَمَا قَالَ ‏.‏