Sahih Muslim 2601
Sahih Muslim · Book 45: The Book of Virtue, Enjoining Good Manners, and Joining of the Ties of Kinship · Whomever Is Cursed, Reviled Or Prayed Against By The Prophet (SAW) When He Does Not Deserve That, It Will Be Purification, Reward And Mercy For Him
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
حَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ ، وَعَبْدُ بْنُ حُمَيْدٍ ، قَالَ زُهَيْرٌ حَدَّثَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ ، حَدَّثَنَا ابْنُ أَخِي ابْنِ شِهَابٍ ، عَنْ عَمِّهِ ، حَدَّثَنِي سَعِيدُ بْنُ الْمُسَيَّبِ ، عَنْ أَبِي هُرَيْرَةَ ، أَنَّهُ قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " اللَّهُمَّ إِنِّي اتَّخَذْتُ عِنْدَكَ عَهْدًا لَنْ تُخْلِفَنِيهِ فَأَيُّمَا مُؤْمِنٍ سَبَبْتُهُ أَوْ جَلَدْتُهُ فَاجْعَلْ ذَلِكَ كَفَّارَةً لَهُ يَوْمَ الْقِيَامَةِ " .
I have held covenant with Thee which Thou wouldst not break, so for any believer whom I curse or beat, make that an expiation on the Day of Resurrection.