Is it permissible to kill cats to ward off their harm from the restaurant and its customers?
Question

                I have a friend who owns a restaurant, and he has started to have a lot of cats at his place; they steal the food and attack his customers. He tried to get rid of them by tranquillizing them and taking them far away, but they came back. The restaurant is being threatened with closure because of these cats. Is it permissible for him in this case to get rid of them by using poison or the like? May Allaah reward you with good.
Praise be to Allah.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. 
They replied: 
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.  
They replied: 
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).