(120) بَابُ الْمُسْلِمُ مَرْآةُ أَخِيهِ
Abu Hurayra reported that the Prophet, may Allah bless him andgrant him peace, said, "A believer is the mirror of his brother. A believeris the brother of another believer. He protects him against loss and defendshim behind his back."
Reference: Al-Adab Al-Mufrad 239
In-book reference: Book 12, Hadith 2
English translation: Book 12, Hadith 239