Short answer
If the animal was still alive when its throat was cut correctly with bismillah, the meat is halal, though painful stunning is disliked. If the stun killed it before the cut, it is carrion and haram, since the Quran forbids animals killed by a violent blow. Because some stunning methods kill animals first, Deobandi institutions advise meat from unstunned slaughter.
An animal must be alive at the moment of slaughter. If stunning killed it first, the meat is haram; if it was alive, the slaughter is valid, though stunning that causes needless pain is makruh. When it is unclear whether stunned animals were alive, Deobandi scholars advise avoiding the meat.
The four schools agree on this.
Explanation
The four schools agree on the principle: an animal killed by a blow is carrion, and the slaughter must happen while it is alive. The Quran names the animal killed by a violent blow (mawqudhah) among the forbidden. Stunning is a modern practice, so the question is how it works in fact.
- Captive bolt (common for cattle): a bolt is fired into the skull. It can kill the animal or leave it unable to recover, so many scholars reject it.
- Electric stunning (common for sheep and poultry): a current makes the animal unconscious. Set correctly, the animal could recover; set too high, some animals die before the cut.
- Gas stunning: animals are made unconscious, and many may die before slaughter.
Halal certifiers differ. Some accept reversible stunning if checks show the animals survive it. Others, including the Deobandi institutions and certifiers who follow them, accept only unstunned meat, because in a busy plant there is no way to know that each animal was alive at the cut, and stunning adds suffering that Islam asks us to avoid.
When you buy halal meat in the West, ask whether it is stunned. Many certifiers state this on their websites. If you want the safest choice, buy meat marked as unstunned or hand slaughtered. See also machine slaughtered chicken and what makes meat halal.
The evidence
Quran, Surah Al-Maaida 5:3
حُرِّمَتْ عَلَيْكُمُ ٱلْمَيْتَةُ وَٱلدَّمُ وَلَحْمُ ٱلْخِنزِيرِ وَمَآ أُهِلَّ لِغَيْرِ ٱللَّهِ بِهِۦ وَٱلْمُنْخَنِقَةُ وَٱلْمَوْقُوذَةُ وَٱلْمُتَرَدِّيَةُ وَٱلنَّطِيحَةُ وَمَآ أَكَلَ ٱلسَّبُعُ إِلَّا مَا ذَكَّيْتُمْ وَمَا ذُبِحَ عَلَى ٱلنُّصُبِ وَأَن تَسْتَقْسِمُوا۟ بِٱلْأَزْلَٰمِ ۚ ذَٰلِكُمْ فِسْقٌ ۗ ٱلْيَوْمَ يَئِسَ ٱلَّذِينَ كَفَرُوا۟ مِن دِينِكُمْ فَلَا تَخْشَوْهُمْ وَٱخْشَوْنِ ۚ ٱلْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِى وَرَضِيتُ لَكُمُ ٱلْإِسْلَٰمَ دِينًۭا ۚ فَمَنِ ٱضْطُرَّ فِى مَخْمَصَةٍ غَيْرَ مُتَجَانِفٍۢ لِّإِثْمٍۢ ۙ فَإِنَّ ٱللَّهَ غَفُورٌۭ رَّحِيمٌۭ ﴿٣﴾
Prohibited to you are dead animals, blood, the flesh of swine, and that which has been dedicated to other than Allah, and [those animals] killed by strangling or by a violent blow or by a head-long fall or by the goring of horns, and those from which a wild animal has eaten, except what you [are able to] slaughter [before its death], and those which are sacrificed on stone altars, and [prohibited is] that you seek decision through divining arrows. That is grave disobedience. This day those who disbelieve have despaired of [defeating] your religion; so fear them not, but fear Me. This day I have perfected for you your religion and completed My favor upon you and have approved for you Islam as religion. But whoever is forced by severe hunger with no inclination to sin - then indeed, Allah is Forgiving and Merciful.
An animal killed by a blow is forbidden, unless slaughtered before it dies.
Sahih Muslim 1955
Sahih... إن الله كتب الإحسان على كل شيء ...
"Allah has prescribed excellence in everything."
Slaughter is to be done with mercy, without needless suffering.
Where the ruling is recorded
- The Islamic Laws of Animal Slaughter (Mufti Taqi Usmani), Chapter on stunning. Why stunning is disliked and when it makes the meat haram.
- al-Fatawa al-Hindiyya, Kitab al-Dhaba'ih. The animal must be known to be alive at the time of slaughter.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.