Full Sharh — Mishkat al-Masabih 2233
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
English Translation
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.
Source
Mishkat al-Masabih(مشكاة المصابيح)
Supplications
Hadith Number
2233