What is meant here is the prohibition of abusing a Muslim whose private affairs are concealed and whose outward conduct appears just and upright. As for the one who has cast aside the garment of modesty and brazenly commits sins, such a person enjoys no protection from back-biting, and insulting him carries no sanctity. Muslim narrated that the Prophet ﷺ said, “All of my community will be pardoned except those who publicize their sins.” [Bukhari 6569; Muslim 2995] They are the people who lay bare their misdeeds, tearing down the veil Allah had placed over them.

His words, “and fighting him is disbelief,” mean that if someone regards it lawful to fight a fellow Muslim, he becomes an unbeliever whose disbelief expels him from the faith, for in doing so he denies clear and authentic scriptural texts. If, however, he does not deem such fighting lawful, then the “disbelief” intended here is that of ingratitude for the blessing, benevolence, and Islamic brotherhood bestowed by Allah. To repudiate these noble Islamic values is a form of thanklessness, a lesser disbelief that does not remove one from Islam. Allah knows best.