Short answer
Islam commands that the animal be slaughtered with as little suffering as possible: a very sharp knife, one swift cut of the throat, no sharpening the blade in front of it and no slaughtering one animal in sight of another. Causing needless pain is sinful. The four schools agree.
Slaughter should cut the windpipe, gullet and both jugular veins with a sharp blade; cutting three of the four is enough for the meat to be halal. It is makruh to cause unnecessary pain: dragging the animal roughly, sharpening the knife before it, cutting to the spinal cord, or skinning or breaking its neck before it has died.
The four schools agree on this.
Explanation
The Prophet ﷺ said that Allah has prescribed excellence in everything, so when you slaughter, slaughter well: sharpen your blade and let the animal be at ease. He once told A'ishah to sharpen the knife on a stone before he sacrificed. The Quran reminds us that the animals are subjected to us so that we glorify Allah and be grateful, not so that we harm them.
- Sharp knife: test it beforehand, away from the animal.
- Calm handling: give water, do not drag it by the leg or the ear, and lay it gently on its left side facing the qiblah.
- One swift cut: through the throat, not sawing back and forth.
- Out of sight: do not slaughter one animal while another watches.
- Wait: do not skin, cut or break the neck until movement has stopped.
- Children watching: fine if they are calm and it is done well; it teaches respect for the meat they eat.
The cut severs the major blood vessels so blood leaves quickly and the animal loses awareness fast; scholars hold this is the most merciful method open to us. On stunning before slaughter, see is stunned meat halal. If you are not experienced, let a trained butcher do it while you are present, which is still your sacrifice. More on the conditions is in what makes meat halal.
The evidence
Quran, Surah Al-Hajj 22:37
لَن يَنَالَ ٱللَّهَ لُحُومُهَا وَلَا دِمَآؤُهَا وَلَٰكِن يَنَالُهُ ٱلتَّقْوَىٰ مِنكُمْ ۚ كَذَٰلِكَ سَخَّرَهَا لَكُمْ لِتُكَبِّرُوا۟ ٱللَّهَ عَلَىٰ مَا هَدَىٰكُمْ ۗ وَبَشِّرِ ٱلْمُحْسِنِينَ ﴿٣٧﴾
Their meat will not reach Allah, nor will their blood, but what reaches Him is piety from you. Thus have We subjected them to you that you may glorify Allah for that [to] which He has guided you; and give good tidings to the doers of good.
The animals are a trust from Allah, slaughtered with gratitude.
Sahih Muslim 1955
Sahih... إن الله كتب الإحسان على كل شيء فإذا قتلتم فأحسنوا القتلة وإذا ذبحتم فأحسنوا الذبح ...
"Allah has prescribed excellence in everything: when you kill, kill well, and when you slaughter, slaughter well. Let one of you sharpen his blade and let his animal be at ease."
Slaughter must be done with the least suffering.
Sahih Muslim 1967
Sahih... يا عائشة هلمي المدية ثم قال اشحذيها بحجر ...
"A'ishah, bring the knife. Then he said: sharpen it on a stone."
The Prophet ensured a sharp blade before his sacrifice.
Where the ruling is recorded
- al-Hidaya, Kitab al-Dhaba'ih, on what is disliked in slaughter. Cutting to the spinal cord, and skinning before the animal cools, are disliked.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Dhaba'ih. Dragging the animal and sharpening the knife in its sight are disliked.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. 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.