Al-Adab Al-Mufrad, Book 24, Hadith 421 (English) ⓘ
'Abdullah said, "When a man says to his companion, 'You are my enemy,' then one of them has left Islam or he is innocent of what his companion said.'"
حَدَّثَنَا شِهَابُ بْنُ عَبَّادٍ، قَالَ: حَدَّثَنَا إِبْرَاهِيمُ بْنُ حُمَيْدٍ الرُّؤَاسِيُّ، عَنْ إِسْمَاعِيلَ، عَنْ قَيْسٍ قَالَ: قَالَ عَبْدُ اللهِ: إِذَا قَالَ الرَّجُلُ لِصَاحِبِهِ: أَنْتَ عَدُوِّي، فَقَدْ خَرَجَ أَحَدُهُمَا مِنَ الإِسْلاَمِ، أَوْ بَرِئ مِنْ صَاحِبِهِ.
also referenced under: Hadith 421 (Reference) & Book 24, Hadith 3 (In-Book)