´It was narrated from Ibn 'Umar that:` 'Uthman said: "I heard the Messenger of Allah [SAW] say: 'It is not permissible to shed the blood of a Muslim except in three cases: A man who commits adultery after having married; or one who kills intentionally, in which case he deserves retaliation; or one who apostatizes after having become Muslim, in which case he deserves to be killed.'"
Explanation & Benefits
Hafiz Muhammad Ameen
(1) The correspondence of the hadith with the chapter heading’s translation is absolutely clear: the ruling for a person who becomes an apostate is that he should be killed.
(2) This statement was made by Hazrat Uthman (radi Allahu anhu) to those rebels who had besieged him, and ultimately, these people martyred him.
(3) If the apostate remains firm upon his apostasy, there is consensus that he will be killed. Hazrat Abu Bakr (radi Allahu anhu) fought against the apostates and killed them without hesitation. No companion objected to this. Thus, there is consensus (ijma‘) of the Companions on this punishment. However, only that person will be called an apostate who explicitly, knowingly commits acts of disbelief, or announces leaving Islam, or joins the disbelievers, or abuses the Messenger of Allah (sallallahu alayhi wa sallam), etc. Due to mutual juristic (fiqhi) differences among Islamic schools of thought, no one will be called an apostate as long as he remains firm upon the fundamentals of the religion.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 4062