(36) باب خَوْفِ الْمُؤْمِنِ مِنْ أَنْ يَحْبَطَ عَمَلُهُ وَهُوَ لاَ يَشْعُرُ
Narrated 'Abdullah:
The Prophet (ﷺ) said, "Abusing a Muslim is Fusuq (an evil doing) and killing him is Kufr (disbelief)."
Reference: Sahih al-Bukhari 48
In-book reference: Book 2, Hadith 41
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 2, Hadith 47