Arabic (Original)
حَدَّثَنَا وَكِيعٌ عَنْ فُضَيْلِ بْنِ غَزْوَانَ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَيُّمَا رَجُلٍ كَفَّرَ رَجُلًا فَأَحَدُهُمَا كَافِرٌ.
English Translation
Waki' narrated to us, from Fudayl ibn Ghazwan, from Nafi', from Ibn 'Umar, who said: The Messenger of Allah, peace and blessings be upon him, said: 'Whenever a man declares another a disbeliever, then one of the two is indeed a disbeliever.'