Arabic (Original)
حَدَّثَنَا ابْنُ نُمَيْرٍ وَحَمَّادُ بْنُ أُسَامَةَ قَالَا حَدَّثَنَا عُبَيْدُ اللَّهِ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ مَنْ كَفَّرَ أَخَاهُ فَقَدْ بَاءَ بِهَا أَحَدُهُمَا.
English Translation
Ibn Numayr and Hammad ibn Usamah told us, they said: Ubaydullah told us, from Nafi', from Ibn Umar, from the Prophet, peace and blessings be upon him, who said: "Whoever declares his brother an unbeliever, then it returns upon one of the two of them."