Abu Huraira reported: The Prophet, peace and blessings be upon him, said, “The believer is a mirror to his faithful brother. He protects him against loss and defends him behind his back.”

Abu Huraira said, “The believer is a mirror to his brother. If he sees something wrong in him, he should correct it.”

Source: al-Adab al-Mufrad 239

Grade: Hasan (fair) according to Al-Albani

“عَنْ أَبِي هُرَيْرَةَ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ‏ : الْمُؤْمِنُ مَرْآةُ أَخِيهِ وَالْمُؤْمِنُ أَخُو الْمُؤْمِنِ يَكُفُّ عَلَيْهِ ضَيْعَتَهُ وَيَحُوطُهُ مِنْ وَرَائِهِ.”

وقال أبو هريرة رضي الله عنه: ْمُؤْمِنُ مَرْآةُ أَخِيهِ إِذَا رَأَى فِيهَا عَيْبًا أَصْلَحَهُ”

((239 الأدب المفرد))