Is it permissible for him to kill practitioners of witchcraft without the permission of the authorities?

Witchcraft is widespread in our land and they annoy and harm the people. Is it permissible to kill them so that the people will be spared their evil? 
Please note that our government allows them to work and takes taxes from them.

Praise be to Allaah.

Firstly: 

If it is proven that a person is doing witchcraft then it is obligatory to kill him because of his evil and the harm that he is doing to people. This has been explained in the answer to question no. 13941. 

What is required of those whom Allaah has placed in authority over people is to rule them in accordance with that which Allaah has revealed. Allaah says (interpretation of the meaning): 

“And so judge (you O Muhammad) among them by what Allaah has revealed and follow not their vain desires”

[al-Maa’idah 5:49] 

“And whosoever does not judge by what Allaah has revealed, such are the Kaafiroon (i.e. disbelievers — of a lesser degree as they do not act on Allaah’s Laws)”

[al-Maa'idah 5:44] 

“And whosoever does not judge by that which Allaah has revealed, such are the Zaalimoon (polytheists and wrongdoers — of a lesser degree)”

[al-Maa’idah 5:45] 

“And whosoever does not judge by what Allaah has revealed (then) such (people) are the Faasiqoon [the rebellious i.e. disobedient (of a lesser degree)] to Allaah”

[al-Maa'idah 5:47] 

It is not permissible at all to annul a punishment prescribed in sharee’ah. Even worse and more abhorrent than that is approving of the haraam deed and allowing the practitioner of witchcraft to work his magic in return for paying taxes. 

This is a betrayal of trust which the ruler will be asked about on the Day of Resurrection, the Day on which he will bite his hand in regret, but it will be to no avail. Allaah says (interpretation of the meaning): 

“And (remember) the Day when the Zaalim (wrongdoer, oppressor, polytheist) will bite at his hands, he will say: ‘Oh! Would that I had taken a path with the Messenger (Muhammad).

28. ‘Ah! Woe to me! Would that I had never taken so‑and‑so as a Khaleel (an intimate friend)!

29. “He indeed led me astray from the Reminder (this Qur’aan) after it had come to me. And Shaytaan (Satan) is to man ever a deserter in the hour of need.’”
[al-Furqaan 25:27-29] 

Secondly: 

If the ruler does not do what is required of him of carrying out punishments prescribed in sharee’ah, then no one of the Muslim masses has the right to do that, because punishments first require proof that this person deserves this punishment, then they require the authority to carry them out. 

If the door is opened for people to carry out the shar’i punishments, chaos will reign in society and no one’s life or wealth will be safe. 

The scholars of the Standing Committee said:  

The one whose job it is to establish proof of witchcraft and carry out those punishments is the ruler who is in charge of the Muslims’ affairs, so as to ward off evil and to close the door to chaos. 

Fataawa al-Lajnah al-Daa’imah (1/552). 

In the answer to question no. 13941 we have quoted the words of Shaykh Sulaymaan al-‘Alwaan:  

Once it is proven that a person is guilty of practicing magic, then he must be killed. This was proven from a group of the Sahaabah, but it is not for individuals to carry out this hadd punishment without the command of the ruler or his deputy, because carrying out the hadd punishments without the authority of the ruler may lead to mischief, and destroy any sense of security in the society, and undermine the position of the ruler. End quote. 

We have mentioned the conditions of the ruler in carrying out hadd punishments in the answer to question no. 8980, where we mentioned that there is scholarly consensus on this point. 

You have to warn the people against this practitioner of witchcraft and against going to him, and explain that this action may lead a person to kufr and going beyond the pale of Islam. 

And Allaah knows best.