The Messenger of Allah ﷺ said, "The believer is the mirror of the believer, and the believer is the brother of the believer. He protects him from loss and guards him from behind."
عن رسول الله ﷺ قال: المؤمن مرآة المؤمن، والمؤمن أخو المؤمن، يكف عليه ضيعته، ويحوطه من ورائه.
This was narrated by Abu Dawud (4918), Bukhari in Adab al-Mufrad (239), and Bazzar (8109), all of them through various routes from Kathir bin Zayd, from Walid bin Rabah, from Abu Hurairah, who mentioned it. Its chain is hasan because of Kathir bin Zayd, who is Aslami, since his hadith is hasan.Tirmidhi (1929) narrated it through another route from Yahya bin Ubaydullah, from his father, from Abu Hurairah, who said, the Messenger of Allah ﷺ said, "Each of you is a mirror for his brother, so if he sees something harmful on him, let him remove it from him." Tirmidhi said, "Shubah declared Yahya bin Ubaydullah daif."I say, it is as he said, for the majority of the scholars declared him daif, and Ibn Hibban said, "He narrates from his father things that have no basis." However, Ibn Adi said, "In some of what he narrates there is material that is not corroborated," meaning that he may be corroborated in some of what he narrates, and this is one such case, strengthened by what came before it.