Praise be to Allaah.
If their harm cannot be warded off except by means of what is mentioned of poisoning them, then that is permissible. The Standing Committee for Issuing Fatwas was asked about the permissibility of killing with poison or other means, especially if they are harmful or causing the transmission of some diseases.
There is nothing wrong with killing cats if they are harmful or carry harmful diseases, if it is not possible to get rid of them by means other than killing.
End quote. Fataawa al-Lajnah al-Daa’imah (16/190).
They were also asked about the ruling on poisoning cats that are found in large quantities in some hospitals, because they harm the patients.
If the situation is as described, that the cats pose a danger and it is not possible to protect the patients from their harm or ward off their evil, and getting rid of their harm can only be done by killing them, then it is permissible to kill them by the easiest means of disposing of them, whether it is by poison, shooting them with bullets, and so on.
Fataawa al-Lajnah al-Daa’imah (26/190).