I would like to reproduce here below paragraphs 330 to 335 from Dr. Muhammad Hamidullah's "The Muslim Conduct of State" in order to elaborate further on this subject. It should be borne in mind that this book is a recognized authority on Muslim International Law and that the law of Apostasy is discussed in the International context:

"To wage war against apostates is justified on the same principle as that on which the punishment of a solitary apostate is based. The basis of Muslim polity being religious and not ethnological or linguistic, it is not difficult to appreciate the reason for penalising the act of apostasy, for it constitutes a politico-religious rebellion. The greater the harm of a given rebellion to a polity, the greater is the severity of repression. Every civilisation, not the least the modern Western one - both in the communistic and capitalistic manifestations - has provided capital punishment against violating the integrity of what it considers its very raison d'etre; and one cannot deny that right to Islam. As an independent organic community, Islam will have the liberty to determine what points should be dearer to it: colour of one's skin, language spoken by its subjects or ideology which animates its existence. As a passing remark, let us recall that the Byzantine law of the epoch of the Prophet also punished with death the apostasy from the Byzantine sect of Christianity. (paragraph 330)

Apostasy in Muslim law means turning from Islam after being a Muslim. Not only does it occur when a person declares his conversion to some non-Islamic religion, but also when he refuses to believe in any and every basic article of the Islamic faith. (paragraph 331)

The sayings and doings of the Prophet, the decision and practice of the Caliph Abu Bakr, the consensus of the opinion of the Companions of the Prophet and all the later Muslim jurisconsults, and even certain indirect verses of the Qur'an, all prescribe capital punishment for an apostate. In the case of apostasy, no distinction is made between a Muslim born of Muslim parents and a convert; and similarly there is no difference between accepting Judaism or Christianity, atheism or idol-worship or any other non-Islamic faith. Nevertheless, Muslim jurists emphasize that before prosecuting and condemning an apostate, it is necessary officially to discuss the matter with him and to remove his doubts regarding the soundness and reasonableness of the Islamic point of view in the matter concerned. Time is given him for reflection sometimes even for months before finally proceeding with the prosecution. There is no difference between a free man and a slave, as Sarakhsiy is explicit. ⁽⁷⁾

In case an insane person, a delirious, a melancholy and perplexed man, a minor, or intoxicated, one who had declared his faith in Islam under coercion, and a person whose faith in Islam has not been known or established were to become apostate, they would not suffer the supreme penalty. So, too, an apostate woman, or a hermaphrodite, according to the Hanafi school of law, would not be condemned to death, but imprisoned and even physically tortured. An old man from whom no offspring is expected is also excepted. (paragraph 333)

TREATMENT OF AN APOSTATE.

The apostate has to choose between Islam and the sword; he cannot be given quarter, nor will he be allowed to become a dhimmi, i.e. a resident non-Muslim subject of the Muslim State, on payment of the yearly protection-tax. (paragraph 334)

De jure he is dead. So if he does not re-embrace Islam, and escapes to some non-Muslim territory, his property in the Islamic territory will be distributed among his Muslim heirs as if he were dead. In addition to this, the debts owed to him will be wiped out if he has reached non-Muslim territory. This is what Mawardi says, but I wonder why these debts should not be inherited by the heirs of the renegade just like the rest of his property." (paragraph 335)

6. Muhammad Hamidullah, The Muslim Conduct of State, Lahore, Pakistan: Sheikh Muhammad Ashraf, 1977, page 6