Praise be to Allaah.
It is essential to stone the married adulterer until he dies, following the Sunnah of the Messenger (peace and blessings of Allaah be upon him), as it is proven that he said that, did it and enjoined it. The Messenger of Allaah (peace and blessings of Allaah be upon him) stoned Maa’iz, the Juhani woman, the Ghaamidi woman, and the two Jews.
The Messenger of Allaah (peace and blessings of Allaah be upon him) stoned (adulterers) and we stoned (them) after him, but I fear that there may come a time when some people say: ‘By Allaah, we do not find the verse of stoning in the Book of Allaah.’ So they will go astray by forsaking an obligation that Allaah has revealed. According to the Book of Allaah, stoning is deserved by the one who commits zina, if he is married, men and women alike, if proof is established or the woman becomes pregnant or they confess…”
Based on this, it is not permissible to replace stoning with killing by the sword or shooting, because stoning is a more severe punishment and a more effective deterrent to the sin of zina, which is the most grave sin after shirk and killing a soul whom Allaah has forbidden us to kill.
“The [unmarried] woman or [unmarried] man found guilty of sexual intercourse - lash each one of them with a hundred lashes, and do not be taken by pity for them in the religion of Allah, if you should believe in Allah and the Last Day. And let a group of the believers witness their punishment."
- 24:2
Wa Allahu alam (Allah knows best). Assalamualaikum, wa rahmatullahi wabarakatu ya ikhwati.