How is a married fornicator to be killed despite not disbelieving through fornication?

The Sunnis argue against theites that a perpetrator of a major sin is not an infidel; otherwise, the prescribed punishment would not be carried out, nor would these punishments be expiations for those on whom they are inflicted. The married fornicator is stoned while being a Muslim, and prayers are offered for him, and his punishment is an expiation for him. The Messenger of Allah, peace and blessings be upon him, carried out the prescribed punishments on Muslims, and these were expiations for them. There is no prescribed punishment or expiation for an infidel or a hypocrite.