The one who apostatizes is called ‘murted’. In orthodox İslamic sense, the punishment for apostasy is death penalty. For this practice which is not stated in the Quran, the so-called hadith “Kill him who changes his religion” (Buhârî, Jihad, 149) is adduced as proof. However, provisions of the Quran, fards, and harams and so on can only be learned from the Quran. Words that are not stated in the Quran or contradict with the Quran do not belong to our prophet.
According to the verse “… He shares His Sovereignty with no one.” (the Kahf, 26) Allah gave no authorization about the sovereignty. “Sovereignty belongs to none but Allah…” (Joseph, 40) Allah who owns the Judgment did not impose an earthly punishment.
The Quran approaches every opinion and belief tolerantly. “There is no force (compulsion) in religion” (Surah Bakara, 256) Nobody has the right to force and apply oppression to those who does not think like themselves. Everybody is free to believe in whatever they choose. As understood in the verse “… Would you, then, compel people, so that they become believers?” (Surah Yunus, 99), to force people to have faith in Allah is an unacceptable attitude in Islam. “So, extend ‘advice and reminder’ if advice and reminder is useful.” (Surah Ala, 9) If it is not useful, then you say “For you is your faith, and for me, my faith” (Surah Kafiroon, 9) and move on.
… Whoever of you turns away from his religion and dies an infidel, such people are those whose deeds will go to waste in this world and in the Hereafter, and they are people of the Fire, they shall be there forever (Surah Bakara, 217) As it can be understood from the verse, if people turn away from their religion, this is their own decision. They live their own choices in this world and die one day. All the deeds they do before they turn away from religion go to waste and they are judged at afterlife. No punishment and sanction is imposed in this world.
Surely, those who believed and then disbelieved, believed again and then disbelieved, then went on increasing in their disbelief… Allah is not to forgive them nor lead them on the path… (Surah Nisa, 137) If you read verse carefully, it mentions about those who believed first and then disbelieved. These people were not murdered after disbelief. Then they believed again. And they disbelieved again. For this phase and for later, Allah imposes no penal sanction.
Whoever kills (unjustly) a person not in retaliation for a person killed, nor for spreading disorder on the earth, is as if he has killed the whole of humankind. (Surah Maide, 32) The provision of the verse is clear. There is no provision about death for nothing but retaliation and war. On the contrary, if someone is murdered for a reason other than retaliation and war, this is held equal to murder of whole mankind. Those who disbelieve after belief harm themselves. And murdering someone just for change their belief is a loss for murderer. Allah approves revival not murder. He does not welcome outrageous and extremer.
Whoever saves the life (by preventing their death) of a person is as if he has saved the life of the whole of humankind. Certainly, Our messengers have come to them with clear signs. Then, after all that, many of them are there to commit excesses on the earth.
(Surah Maide, 32)