What is the ruling regarding a Muslim who kills a large number of Muslims: does he become an infidel and abide in Hellfire eternally, or is he considered a disobedient Muslim? And does his ruling differ from that of one who kills a single Muslim?

Killing a Muslim intentionally and aggressively is a grave sin and a tremendous transgression. The crime escalates with an increase in killings. The texts of the Quran and Sunnah (definition) have consistently emphasized the enormity of this crime. Among these texts are: "And whoever kills a believer intentionally, his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment." (Quran 4:93) and "whoever kills a soul unless for a soul or for corruption [done] in the land - it is as if he had slain mankind entirely." (Quran 5:32). And the Prophet, peace and blessings be upon him, said: "If the inhabitants of the heavens and the inhabitants of the earth were to participate in shedding the blood of a believer, Allah would surely cast them into the Fire." As for ruling that the killer is a disbeliever, the preponderant opinion is that it is a disbelief short of the disbelief that expels one from the fold of Islam. Scholars have interpreted the Hadith (definition), "Insulting a Muslim is wickedness, and fighting him is disbelief," in several ways, including that it applies to one who considers it lawful, or it is a disbelief in goodness and blessing, or it leads to disbelief due to its ominous nature, or it is like the actions of disbelievers.