Other than jihad against the Idolaters, fighting is divided into three categories: fighting apostates, fighting wrongdoers, and fighting those who make war. The first category is fighting apostates, namely, when people whose Islam has been ordained for them apostate – either those who have been born into the innate disposition [fitra] of Islam, or those who have yielded into Islam out of prior disbelief; both groups fall equally under judgment of apostasy. If they have apostatized from Islam and converted to any religion whose adherents are permitted to remain in it, like Judaism and Christianity, or whose adherents are not permitted to remain in it, like atheism [zandaqa] or idol worship [wathaniya, paganism], it is not permitted for someone who has apostatized to remain there, given that remaining in the truth necessitates abiding by its precepts; the Messenger of Allah (SAW) said: "Whoever changes his religion, kill him." Whenever they are of those whose killing is necessitated because they have apostatized from the religion of truth into any other religion, they unavoidably fall into one of two situations:
1) When they are out of the way and isolated in Islamic territory [Dar Al-Islam], and have not withdrawn into a place which would single themselves out from the Muslims, we have no need to fight them in order for them to be subdued and to reveal the reason for their apostasy. … But whoever remains firm in his apostasy and does not repent must be killed, men and women. Abu Hanifa said: I would not kill a woman for apostasy. However the Messenger of Allah (SAW) killed a woman known as Umm Ruman for apostasy. … The legal scholars have differed regarding killing them – must it be carried out immediately or may it be delayed for three days? – into two points of view. One calls for it to be carried out immediately, lest any obligation to Allah Mighty and Sublime be delayed. The second is to watchfully wait for three days, that perchance they may correct him through repentance. ‘Ali (peace be upon him) admonished Al-Mustawrid Al-‘Ijli to repentance for three days, then killed him afterwards. And as a captive one is to be killed by the sword, although Ibn Suraij, one of the companions of Al-Shafi’i, said: They are to be beaten with a wooden stick until they die, since this is a slower killing than by a hasty sword, and they may thereby be corrected unto repentance. ...
2) The second situation is that they withdraw to a certain place in order to isolate themselves from the Muslims to the point of becoming unattainable there; they must be fought for their apostasy, after speaking to them about Islam and making its evidence clear. Fighting is engaged with them, after warning and formal notice, in the same way as for fighting people in war territory [ahl al-harb], who are fought by trickery, by night, or openly lined up for battle; they can be fought from the front or from behind.