Any person who called his brother: "O unbeliever" (has in fact done an act by which this unbelief) would return to one of them. If it were so, as he asserted (then the unbelief of man was confirmed but if it was not true), then it returned to him (to the man who labeled it on his brother Muslim).  

قَالَ رَسُولُ اللَّهِ ﷺ أَيُّمَا امْرِئٍ قَالَ لأَخِيهِ يَا كَافِرُ فَقَدْ بَاءَ بِهَا أَحَدُهُمَا إِنْ كَانَ كَمَا قَالَ وَإِلاَّ رَجَعَتْ عَلَيْهِ  

Malik related to me from Abdullah ibn Dinar from Abdullah ibn Umar that the Messenger of Allah ﷺ said, "If a man says to his muslim brother, 'O kafir!' it is true about one of them."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ مَنْ قَالَ لأَخِيهِ يَا كَافِرُ فَقَدْ بَاءَ بِهَا أَحَدُهُمَا  

[Machine] He informed him that the Messenger of Allah ﷺ said: "If a person calls his companion 'O disbeliever', then it will apply to one of them. If the one to whom it was said is a disbeliever, then he is a disbeliever, but if not, then it returns to the one who said it."  

أَخْبَرَهُ أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِذَا قَالَ الرَّجُلُ لِصَاحِبِهِ يَا كَافِرُ فَإِنَّهَا تَجِبُ عَلَى أَحَدِهِمَا فَإِنْ كَانَ الَّذِي قِيلَ لَهُ كَافِرٌ فَهُوَ كَافِرٌ وَإِلَّا رَجَعَ إِلَيْهِ مَا قَالَ  

[Machine] The Messenger of Allah ﷺ said: "Whoever says to his brother, 'O disbeliever,' one of them has indeed earned it."  

قَالَ رَسُولُ اللهِ ﷺ مَنْ قَالَ لِأَخِيهِ يَا كَافِرُ فَقَدْ بَاءَ بِهَا أَحَدُهُمَا  

[Machine] On the authority of the Prophet ﷺ , he said: When a man says to his brother, "You are a disbeliever" or "O disbeliever," then one of them has brought it upon himself.  

عَنِ النَّبِيِّ ﷺ أَنَّهُ قَالَ إِذَا قَالَ الرَّجُلُ لِأَخِيهِ أَنْتَ كَافِرٌ أَوْ يَا كَافِرُ فَقَدْ بَاءَ بِهَا أَحَدُهُمَا  

[Machine] From the Prophet ﷺ that he said, "When a man says to another man, 'O disbeliever,' then one of them will bear the consequences of what he said, if it is as he described. Otherwise, it will return upon the other."  

عَنِ النَّبِيِّ ﷺ أَنَّهُ قَالَ إِذَا قَالَ الرَّجُلُ لِلرَّجُلِ يَا كَافِرُ فَقَدْ بَاءَ بِهِ أَحَدُهُمَا إِنْ كَانَ كَمَا قَالَ وَإِلَّا رَجَعَتْ عَلَى الْآخَرِ  

Any person who called his brother: "O unbeliever" (has in fact done an act by which this unbelief) would return to one of them. If it were so, as he asserted (then the unbelief of man was confirmed but if it was not true), then it returned to him (to the man who labeled it on his brother Muslim). (Using translation from Muslim 60b)  

قَالَ رَسُولُ اللَّهِ ﷺ «أَيُّمَا امْرِئٍ قَالَ لِأَخِيهِ كَافِرٌ فَقَدْ بَاءَ بِهِ أَحَدُهُمَا إِنْ كَانَ كَمَا قَالَ وَإِلَّا رَجَعَتْ عَلَيْهِ»  

"أيُّمَا امْرِئ قَال لأخيه "كَافِرٌ" فَقَدْ بَاءَ بها أحَدُهُمَا إِنْ كَانَ كمَا قَال، وَإلا رَجَعتْ عَلَيهِ ".