You have quoted only two incidents outside the battlefield, which make a person liable for ‘qatal’ (capital punishment). But is a ‘murtad’ also not ‘Wajib -ul Qatal’? We also have the incident in Medina, when Hazrat Omer (ra) killed a so-called Muslim, who had earlier shown reluctance to accept the verdict given by Rasoolullaah (saw).
I have also mentioned in my statement that the Quran has clearly declared that if a person is killed for any reason other than these two reasons, then it would be deemed as if the entire mankind has been killed. [Emphasis: the Quran]
After such a clear mention in the Quran, if there is some information which apparently goes against it, it should either be explained in the light of the Quran so that it conforms to its principles or should be rejected.
The claim that Omer, radiallahu anhu, killed a person who declined to accept the verdict of the prophet, alaihissalaam, is baseless because it is not coming from an authentic source, and also because the verse which it is claimed was revealed to absolve him, is saying nothing to support the act of killing by anyone. The verse reads like this:
“Nay! (O Messenger) – by your Lord – they will never be true believers until they accept you as a judge in their disputes, then they do not find any resentment in their hearts against your verdicts and accept them with complete submission.” (4:65)
As for the claim that an apostate (Murtad) is to be killed, it is based on the following hadith:
“Whoever changed his Islamic religion, then kill him.” (al-Bukhari)
This hadith is absolutely correct and based directly on the Quranic instruction that all polytheists (al-Mushrikun) who rejected the prophet, alaihissalaam, were to be killed after a certain duration, according to the Almighty’s law that the rejecters of His messengers (al-Rusul) have to face the punishment of death in this life, if they are polytheists (in obvious and conscious denial of the truth).
The Quran says:
“Then, when the sacred months have passed, kill the polytheists wherever you find them.” (9:5)
Obviously if a person was to be killed for not being a Muslim in the first place, if he becomes a non-Muslim after converting to Islam, he should still be killed. However, this punishment has nothing to do with the ordinary non-Muslims of any other times as indeed the instruction “kill the polytheists wherever you find them” has nothing to do with the polytheist of any other times.