“Admonish therefore, for thou art but an admonisher. Thou hast no authority to compel them.”
Holy Qur'an 88:22-23
The Qur'an is explicit in many places that belief is a matter of the heart, and not something that can be forced or controlled externally. The Qur'an prescribes no punishment whatsoever to be administered to those who give up religious beliefs. Indeed, it is the freedom of choice in having religious beliefs in the first place that makes them worthy of merit.
Islam does not allow the taking of life of a person simply because he is a non-Muslim or has gone back from Islam to disbelief. The golden rule of Islam is: "there is no compulsion in religion" (2:257). Allah says in the Holy Quran:
"And say: 'It is the truth from your Lord; -wherefore let him who will, believe, and let him who will, disbelieve"(18:30).
'Say: 'O Ye men, now has the truth come to you from your Lord. So whosoever follows the guidance, follows it for the good of his own soul, and whosoever errs, errs only against it. And I am not a keeper over you"(10:109).
These verses show clearly that in the matter of faith everyone is free in the choice of one's religion. There cannot possibly be any compulsion in preventing people from accepting or renouncing Islam. Had it been proper to use force in any shape or form in the matter of religion, God Himself would have forced the people to enter Islam and to renounce all other faiths. God says in the Holy Quran:
"And if thy Lord had enforced His Will, surely all men on the earth would have believed together. Wilt thou, then, force men to become believers?"(10:100).
The Holy Quran has, on no occasion, prescribed death penalty for the apostates. Let us refer to some verses of the Holy Quran in this context:
"Whoso disbelieves in Allah after he has believed—save him who is forced thereto while his heart finds peace in the faith, — but such as open their breasts to disbelief, on them is Allah's Wrath; and they shall have a severe punishment. That is because they have preferred the present life to the Hereafter, and because Allah guides not the disbelieving people."(16:107, 108)
"Those who believe, then disbelieve, then again believe, then disbelieve, and then increase in disbelief, Allah will never forgive them nor will He guide them to the way."(4:138)
"And they will not cease fighting you until they turn you back from your faith, if they can. And whoso from among you turns back from his faith and dies while he is a disbeliever, it is they whose work shall be vain in this world and the next. These are the inmates of the fire and therein shall they abide."(2:218).
"Oh Ye who believe! whoso among you turns back from his religion, then let it be known that in his stead Allah will soon bring a people whom He will love and who will love Him; and who will be kind and humble towards believers, hard and firm against disbelievers. They will strive in the cause of Allah and will not fear the reproach of a fault-finder. That is Allah's grace: He bestows it upon whomsoever He pleases; and Allah is bountiful, All-Knowing."(5:55).
"And he who turns back on his heels, shall not harm Allah at all. And Allah will certainly reward the grateful."(3:145).
"And whosoever takes disbelief in exchange for belief, has undoubtedly gone astray from the right path."(2:109).
"Many of the people of the Book wish out of sheer envy from their own selves that, after you have believed, they could turn you again into disbelievers after the truth has become manifest to them. But forgive and turn away from them, till Allah brings about His decree. Surely, Allah has the power to do all that He wills.(2:110)
"And whoso seeks a religion other than Islam, it shall not be accepted from him, and in the life to come he shall be among the losers."(3:86).
"How shall Allah guide a people who disbelieved after their believing and after they had borne witness that the Apostle was true." "Of such the reward is that on them shall be the curse of Allah and of angels and of men, all together. "They shall abide thereunder. Their punishment shall not be lightened nor shall they be reprieved; except those who repent thereafter and amend. And surely, Allah is most Forgiving, Merciful."(3:87-90).
Nowhere in the Holy Quran has it been laid down that an apostate is to be put to death. When we turn to Ahadith (sayings of the Holy Prophet) we find that he did not prescribe death penalty for the apostates.
There can be no true Hadith in contradiction to the Holy Quran. The Holy Prophet had said that whenever anyone wanted to quote any saying of his, one should see whether it was in accordance with the Holy Quran.
If so, then it would be from him, otherwise not. Thus it is quite clear from the Holy Quran that there is no physical punishment for an apostate in this world.