The claim: "Islam stones adulterers to death; this is barbaric."
The Qur'an's penalty for adultery: not death
- The Qur'an's only penalty for zinā is a hundred lashes, not death: "The adulteress and the adulterer — give each of them a hundred lashes." (24:2)
- Decisive proof: the Qur'an sets half the penalty for an enslaved woman in zinā (4:25). For a penalty to have a half, it must be countable/corporal — death has no half. So the penalty the Qur'an sets is not death.
- The penalty for false accusation (qadhf) is also corporal: eighty lashes (24:4).
So stoning is not in the Qur'an.
An honest limit
Fact: the Qur'an sets lashes, not stoning, for adultery; stoning is a matter of hadith and classical fiqh. Inference / opinion: "can a hadith replace and intensify the Qur'an's stated penalty with death?" — that is an interpretive / methodological debate. As this platform's line is Qur'an-centred: the penalty in the text is lashing; the claim "Islam commands stoning for adultery" is not based on the Qur'an.
Source: Qur'anic verses (M. Okuyan meal). Presented soberly and respectfully, with a text/interpretation distinction.