All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
If stunning the animal before the slaughter ends its life or makes it in a state similar to that of the slaughtered animal, its meat is unlawful to eat since it is considered dead meat. Moreover, cutting the windpipe, the esophagus, the jugular veins, and carotid arteries, after the stunning, isn`t Islamic form of slaughter, because the latter form is what makes the animal`s meat lawful to eat. In addition, it isn`t permissible to slaughter an animal which is already dead.
However, if the stunning renders the animal unconscious but remains alive in the sense that it could wake up after some time, then slaughtering it while in such state is considered an Islamic form of slaughter. Butchers use this technique (stunning) out of mercy to the animal and to facilitate the slaughtering process. Consequently, if the stunning doesn`t kill the animal, then it is permissible to eat the meat of the animal which remained alive after the stunning and was slaughtered according to the Islamic form.
We advise butchers to fear Allah and handle those animals in a humane manner before the slaughter so as to control them as painless as possible, and to use a very sharp knife to swiftly cut the esophagus, windpipe, jugular veins, and carotid arteries. This is attested to in the following narration: Shaddid b. Aus said: "Two are the things which I remember Allah's Messenger (PBUH) having said: "Verily Allah has enjoined goodness to everything; so when you kill, kill in a good way and when you slaughter, slaughter in a good way. So every one of you should sharpen his knife, and let the slaughtered animal die comfortably." {Related by Muslim}.
We remind the butchers that the name of Allah has to be called upon the slaughter of each animal separately since this is a confirmed Sunnah of the Prophet (PBUH). Rather, some scholars stated that it is an obligation. However, the reliable opinion of our school (Shafie) is that it is Sunnah mustahabah and leaving it doesn`t make the meat of such animal unlawful to eat for Allah`s name is engraved in the heart of every Muslim. In addition, there is no evidence in the texts of Sharia (Quran and Prophetic Sunnah) that not invoking Allah`s name upon slaughtering an animal renders its meat unlawful to eat. Our eminent scholars commented on verse 3, Chapter Al-Mai`da (unless ye are able to slaughter it (in due form), "It means that it is lawful to eat the meat of the animal slaughtered in Islamic form although Allah`s name hasn`t been invoked on it."
As for verse 121, Chapter Al-An`am, which states: (Eat not of (meats) on which God’s name hath not been pronounced: That would be impiety. But the evil ones ever inspire their friends to contend with you if ye were to obey them, ye would indeed be Pagans.), many interpreters said that this verse refers to the animals dedicated unto other than Allah. For more information, check [Tafseer At-Tabari vol.12, pp.83]. And Allah the Almighty knows best.