Al-Adab Al-Mufrad
Al-Adab Al-Mufrad 440
حَدَّثَنَا سَعِيدُ بْنُ دَاوُدَ، قَالَ: حَدَّثَنَا مَالِكٌ، أَنَّ نَافِعًا حَدَّثَهُ، أَنَّ عَبْدَ اللهِ بْنَ عُمَرَ أَخْبَرَهُ، أَنَّ رَسُولَ اللهِ صلى الله عليه وسلم قَالَ: إِذَا قَالَ لِلْآخَرِ: كَافِرٌ، فَقَدْ كَفَرَ أَحَدُهُمَا، إِنْ كَانَ الَّذِي قَالَ لَهُ كَافِرًا فَقَدْ صَدَقَ، وَإِنْ لَمْ يَكُنْ كَمَا قَالَ لَهُ فَقَدْ بَاءَ الَّذِي قَالَ لَهُ بِالْكُفْرِ.
Unreviewed translation. All hadiths in this collection are available in five languages. Titles and introductions may remain in Arabic.
Sa‘id ibn Dawud narrated to us: Malik narrated to us, that Nafi‘ informed him, that ‘Abd Allah ibn ‘Umar informed him that the Messenger of Allah (may Allah bless him and grant him peace) said: When someone says to another, ‘Unbeliever!’ one of the two has fallen into disbelief. If the person he called an unbeliever is in fact one, he spoke the truth; but if the other is not as he claimed, then the charge of disbelief returns upon the one who made it.
Notes and open questions — unreviewed
The Arabic makes the return of the charge conditional: if the person addressed is not as the speaker claimed, the charge returns to the speaker.