It is narrated from Sayyiduna Sa'd bin Malik (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "Abusing a Muslim is wickedness and a sin."
Hadith Referenceالادب المفرد / كتاب السباب / 429
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه النسائي ، كتاب المحاربة ، باب قتال المسلم : 4110 و ابن ماجه : 3941»
Explanation & Benefits
Shaykh Maulana Usman Muneeb
Benefits and Issues: To reproach a person for a defect or to attribute to him a blameworthy matter which is not found in him is called abuse (insult). In the second case, it becomes a major sin (kabirah) because it is slander (buhtan).
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 429