Sahih al-Bukhari 6103
صحيح البخاري#6103Sahihحَدَّثَنَا مُحَمَّدٌ، وَأَحْمَدُ بْنُ سَعِيدٍ، قَالاَ حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ، أَخْبَرَنَا عَلِيُّ بْنُ الْمُبَارَكِ، عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِذَا قَالَ الرَّجُلُ لأَخِيهِ يَا كَافِرُ فَقَدْ بَاءَ بِهِ أَحَدُهُمَا ". وَقَالَ عِكْرِمَةُ بْنُ عَمَّارٍ عَنْ يَحْيَى، عَنْ عَبْدِ اللَّهِ بْنِ يَزِيدَ، سَمِعَ أَبَا سَلَمَةَ، سَمِعَ أَبَا هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم.
Narrated Abu Huraira: Allah's Messenger (ﷺ) said, "If a man says to his brother, O Kafir (disbeliever)!' Then surely one of them is such (i.e., a Kafir)
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 78:130