Even historians describe it as "waq`atu 'r-ridda -- the event of apostasy". Although we do not agree with the accusation leveled against some of those who were killed as "apostates,"18 but the justification presented by the caliphate shows that the Sunnis also agree with the Sh`iah fiqh on punishment for those who become murtad.
The Sunni author of the authoritative al-Fiqh `ala 'l-Madhāhibi 'l-Arba`ah writes, "The four (Sunni) Imams agree that it is obligatory to kill a person whose apostasy against Islam is proven."19 The Sunni jurists, however, do not differentiate neither between the fitri and the milli apostate, nor between male and female apostate.20
18. Some such "apostates" like Mālik bin Nuwayrah did not recognize Abu Bakr as the legitimate successor of the Prophet of Islam, and therefore refused to pay zakāt to him. He was brutally killed by Khālid bin Walid who then took Mālik's wife as his own. There was serious disagreement Abu Bakr and `Umar ibn Khattāb on Khālid bin Walid's un-Islamic and inhuman behavior. This is a very well known fact to the students of Muslim history.
19. `Abdu 'r-Rahmān al-Jazairi, al-Fiqh `ala 'l-Madhāhibi 'l-Arba`ah, vol. 5, p. 423-425.
20. Ibn Rushd al-Hafid al-Andulsi, Bidāyatu 'l-Mujtahid wa Nihāyatu 'l-Muqtasid, vol. 2 (Cairo: Maktaba al-Khanji, 1994) p. 383. Abu Hanifah, however, believes that a woman apostate should not be killed.