Hadith 7:108
Jundub said that God’s messenger told of a man saying, “I swear by God that God will not forgive so and so,” whereupon God most high said, “Who is this who swears that I will not forgive so and so? For I have forgiven so and so and have made your deeds to come to nothing”, or words to that effect. Muslim transmitted it.
وَعَنْ جُنْدُبٍ رَضِيَ اللَّهُ عَنْهُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ حَدَّثَ: " أَنَّ رَجُلًا قَالَ: وَاللَّهِ لَا يَغْفِرُ اللَّهُ لِفُلَانٍ وَأَنَّ اللَّهَ تَعَالَى قَالَ: مَنْ ذَا الَّذِي يَتَأَلَّى عَلَيَّ أَنِّي لَا أَغْفِرُ لِفُلَانٍ فَإِنِّي قَدْ غَفَرْتُ لِفُلَانٍ وَأَحْبَطْتُ عَمَلَكَ " أَوْ كَمَا قَالَ. رَوَاهُ مُسلم
Original Reference: Mishkat al-Masabih 2334