[Undertoad]

They are not honour killings then, they are just killings. Via Wikipedia:

In accordance with hadith, stoning to death is the penalty for married men and women who commit adultery. In addition, there are several conditions related to the person who commits it that must be met. One of the difficult ones is that the punishment cannot be enforced unless there is a confession of the person, or four male eyewitnesses who each saw the act being committed. All of these must be met under the scrutiny of judicial authority.

For unmarried men and women, the punishment prescribed in the Qur'an and hadith is 100 lashes.[115]

The "four witness" standard comes from the Qur'an itself, a revelation Muhammad announced in response to accusations of adultery leveled at his wife, Aisha: "Why did they not produce four witnesses? Since they produce not witnesses, they verily are liars in the sight of Allah."[Qur'an 24:13]

Punishments are authorized by other passages in the Qur'an and hadiths for certain crimes (e.g., extramarital sex, adultery), and are employed by some as rationale for extra-legal punitive action while others disagree:

“The woman and the man guilty of adultery or fornication—flog each of them with hundred stripes: Let no compassion move you in their case, in a matter prescribed by God, if ye believe in God and the last day.”[Qur'an 24:2] “Nor come nigh to adultery: for it is a shameful (deed) and an evil, opening the road (to other evils).”[Qur'an 17:32]

In most interpretations of Sharia, conversion by Muslims to other religions, is strictly forbidden and is termed apostasy. Muslim theology equates apostasy to treason, and in most interpretations of Sharia, the penalty for apostasy is death. During the time of Muhammad, treason and apostasy were considered one and the same; nowadays, many scholars differentiate between treason and apostasy, believing that the punishment for apostasy is not death, while the punishment for treason is death.