Jami` at-Tirmidhi 2637
جامع الترمذي#2637Sahihحَدَّثَنَا قُتَيْبَةُ، عَنْ مَالِكِ بْنِ أَنَسٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " أَيُّمَا رَجُلٍ قَالَ لأَخِيهِ كَافِرٌ فَقَدْ بَاءَ بِهِ أَحَدُهُمَا " . هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ غَرِيبٌ . وَمَعْنَى قَوْلِهِ بَاءَ يَعْنِي أَقَرَّ .
Narrated Ibn 'Umar:Ibn 'Umar narrated that the Prophet (ﷺ) said: "Whoever says to his brother 'disbeliever' then it will have settled upon one of them." Sahih
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:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 40:32