Al-Adab Al-Mufrad
Al-Adab Al-Mufrad 439
حَدَّثَنَا إِسْمَاعِيلُ، قَالَ: حَدَّثَنَا مَالِكٌ، عَنْ عَبْدِ اللهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللهِ بْنِ عُمَرَ، أَنَّ رَسُولَ اللهِ صلى الله عليه وسلم قَالَ: أَيُّمَا رَجُلٌ قَالَ لأَخِيهِ: كَافِرٌ، فَقَدْ بَاءَ بِهَا أَحَدُهُمَا.
Unreviewed translation. All hadiths in this collection are available in five languages. Titles and introductions may remain in Arabic.
Isma‘il narrated to us: Malik narrated to us, from ‘Abd Allah ibn Dinar, from ‘Abd Allah ibn ‘Umar, that the Messenger of Allah (may Allah bless him and grant him peace) said: Any man who says to his brother, ‘You are an unbeliever,’ then one of the two has incurred it.
Notes and open questions — unreviewed
The Arabic says one of the two has incurred the charge of disbelief; it does not specify which one.