And they [unbelievers] will not cease from fighting against you till they have made you renegades from your religion, if they can. And whoso becometh a renegade and dieth in his disbelief: such are they whose works have fallen both in the world and the Hereafter. Such are rightful owners of the Fire: they will abide therein. (2:217)
Although this says nothing about killing apostates, many prominent Qur’an commentators make mention of the punishment in their discussions of this verse.
Abu Abdullah al-Qurtubi (d.1273) writes:
Scholars disagree about whether or not apostates are asked to repent. One group say that they are asked to repent and, if they do not, they are killed. Some say they are given an hour and others a month. Others say that they are asked to repent three times, and that is the view of Malik. Al-Hasan said they are asked a hundred times. It is also said that they are killed without being asked to repent.
Note that despite the scholarly disagreement Qurtubi refers to here, he does not cite any authorities who believe that apostates should not be executed.
A more modern scholar, Muhammad Shafi, who was the former Mufti of Pakistan and taught interpretation of the Qur’an for many years until his death in 1979, wrote the following in his extremely popular Urdu-language commentary on the Qur’an:
In short, the fate of an apostate is worse than that of an original disbeliever. This is why Jizya [discriminatory poll tax levied on non-Muslims in an Islamic state] can be accepted from an original disbeliever while a male apostate who does not return to Islam is killed. If the apostate is a woman, she is imprisoned for life. The reason is that their conduct insults Islam and the insult of such a binding authority deserves no less a punishment.
This draconian punishment is taken for granted by Islamic scholars because of the justification that can be found for it in the hadith. In a number of traditions, the Prophet of Islam is reported to have unambiguously commanded: “Whoever changes his Islamic religion, then kill him.” (Sahih Bukhari v.9, b.88, no.6922, and others)
Other hadith contain confirmations of this teaching, and even an example of Muhammad putting it into practice:
Allah's Apostle said, “The blood of a Muslim who confesses that none has the right to be worshipped but Allah and that I am His Apostle, cannot be shed except in three cases: In Qisas [recompense] for murder, a married person who commits illegal sexual intercourse [i.e. an adulterer] and the one who reverts from Islam (apostate) and leaves the Muslims.” (Bukhari v.9, b.83, no.17)
Some Zanadiqa (atheists) were brought to 'Ali and he burnt them. The news of this event reached Ibn 'Abbas who said, “If I had been in his place, I would not have burnt them, as Allah's Apostle forbade it, saying, 'Do not punish anybody with Allah's punishment (fire).' I would have killed them according to the statement of Allah's Apostle, 'Whoever changed his Islamic religion, then kill him.'” (Bukhari v.9, b.84, no.57)
A man embraced Islam and then reverted back to Judaism. Mu'adh bin Jabal came and saw the man with Abu Musa. Mu'adh asked, “What is wrong with this (man)?” Abu Musa replied, “He embraced Islam and then reverted back to Judaism.” Mu'adh said, “I will not sit down unless you kill him (as it is) the verdict of Allah and His Apostle.” (Bukhari v.9, b.89, no.271, and others)
Some people from the tribe of 'Ukl came to the Prophet and embraced Islam. The climate of Medina did not suit them, so the Prophet ordered them to go to the (herd of milch) camels of charity and to drink, their milk and urine (as a medicine). They did so, and after they had recovered from their ailment (became healthy) they turned renegades (reverted from Islam) and killed the shepherd of the camels and took the camels away. The Prophet sent (some people) in their pursuit and so they were (caught and) brought, and the Prophet ordered that their hands and legs should be cut off and that their eyes should be branded with heated pieces of iron, and that their cut hands and legs should not be cauterized, till they die. (Bukhari v.8, b.82, no.794, and others)
In another incident, recounted by the Prophet’s earliest biographer Ibn Ishaq (d.773), Muhammad pronounced a death sentence on a man named Abdullah ibn Sa’d, who “had been a Muslim and used to write down revelation; then he apostatized and returned to Quraysh [Muhammad’s former tribe]” in Mecca. In the end, the punishment was never actually carried out, but this was only because of a bizarre mix-up between Muhammad and his followers:
They allege that the apostle remained silent for a long time till finally he said yes [granting Abdullah immunity from the execution order]. When [Abdullah] had left he said to his companions who were sitting around him, ‘I kept silent so that one of you might get up and strike off his head!’ One of the Ansar [followers] said, ‘Then why didn't you give me a sign, O apostle of God?’ He answered that a prophet does not kill by pointing.
Based on these texts and others like them, there is a scholarly consensus among all the major schools of Islamic law, both Sunni and Shi’ite, that apostates should be killed. The medieval jurist Ibn Rushd (d.1198), better known in the West as the great Muslim philosopher Averroes, summarised this consensus thusly:
An apostate…is to be executed by agreement in the case of a man, because of the words of the Prophet, “Slay those who change their din [religion].”…Asking the apostate to repent was stipulated as a condition…prior to his execution.
Even the lionised Muslim mystic Abu Hamid al-Ghazali (d.1111), who is often hailed as one of the all-time great Muslim thinkers, supported the death penalty for apostasy. For example, here is a statement from al-Ghazali’s discussion of what to do with a “secret apostate”, or one who tries to conceal his newfound unbelief:
The meaning of ‘repentance’ of an apostate is his abandoning of his inner religion. The secret apostate (zindiq) does not give up his inner confessions when he professes the words of the shahada [the Islamic profession of faith, “There is no God but Allah and Muhammad is his Messenger”]. He may be killed for his unbelief because we are convinced that he stays an unbeliever who sticks to his unbelief.
Finally, the classic Islamic legal manual Reliance of the Traveller, which has been endorsed as a reliable guide to sharia law by Cairo’s al-Azhar University, has this to say on the subject of apostasy:
Leaving Islam is the ugliest form of unbelief (kufr) and the worst...When a person who has reached puberty and is sane voluntarily apostatizes from Islam, he deserves to be killed.
In such a case, it is obligatory for the caliph (or his representative) to ask him to repent and return to Islam. If he does, it is accepted from him, but if he refuses, he is immediately killed...There is no indemnity for killing an apostate (or any expiation, since it is killing someone who deserves to die).
What all of the above demonstrates is that despite the claims of some apologists that there is some sort of “controversy” or “debate” within Islam about this particular point, Islamic law and tradition are actually extremely clear: If you are a Muslim and then you decide that you no longer believe in Muhammad and the Qur’an, you must be killed.