Short answer
It depends on the reason. Putting an animal down for convenience, cost of food or because you are moving is not allowed. If a vet says the animal is in severe pain with no realistic cure, many Hanafi scholars allow ending its life in the most painless way, out of mercy. Rehoming is always better than killing a healthy pet.
Killing an animal without a valid need is haram. Ending the life of an animal in severe, incurable suffering, by a quick and painless method, is permitted according to many contemporary Hanafi muftis, by analogy with the classical permission to slaughter a harmful animal with a sharp knife rather than torment it.
The four schools agree on this.
Explanation
Islam teaches deep mercy to animals. The Prophet ﷺ told of a woman who entered the Fire because she locked up a cat until it died, and a man who was forgiven for giving water to a thirsty dog. He also said that Allah has prescribed excellence in everything, so when you kill, kill well. An animal's life is not ours to end for no reason.
Situations people ask about:
- Healthy pet you can no longer keep: putting it down is not allowed. Rehome it with family, friends or a shelter.
- Old age with manageable problems: keep caring for it while it can live without great suffering.
- Terminal illness or severe injury with constant pain: if a vet confirms there is no realistic treatment, many Hanafi scholars allow euthanasia to end its suffering, done by a vet with a painless method.
- An animal that is dangerous: a dog that attacks people may be put down to prevent harm.
The classical Hanafi books say that a cat that harms people should not be beaten or tormented, but slaughtered with a sharp knife. The point is that when an animal must die, it must die without cruelty. Contemporary muftis apply the same mercy to animals in hopeless pain.
This ruling is about animals only. Ending a human life, even to stop suffering, is a different matter and is not allowed; see euthanasia in Islam. Because each case depends on the vet's report, ask a mufti if you are unsure. See also rights of animals.
Ask a mufti about your own case. This answer explains the general ruling. When the details of your situation matter, as they do here, ask a qualified mufti and give them the full facts. Where to ask a scholar.
The evidence
Sahih Muslim 1955
Sahih... إن الله كتب الإحسان على كل شىء فإذا قتلتم فأحسنوا القتلة ...
"Allah has prescribed excellence in everything, so when you kill, kill well."
If an animal must die, it must be done mercifully.
Sahih al-Bukhari 3482
Sahih... عذبت امرأة في هرة سجنتها حتى ماتت ...
"A woman was punished because of a cat she locked up until it died."
Cruelty and neglect towards animals are grave sins.
Where the ruling is recorded
- al-Fatawa al-Hindiyya, Kitab al-Karahiyya, chapter on animals. A harmful cat is not tormented but slaughtered with a sharp knife.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Hazr wa al-Ibaha, on killing harmful animals. Killing animals without need is forbidden; harmful ones may be killed without torment.
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.