Sheikh `Abd al-Rahmân `Alûsh
It is a part of faith to maintain good ties with our relatives. Allah will reward those who maintain these ties and punish those who do not. However, if one of these relatives hurts people and engages in such evil as black magic, then he will not be eligible for such good relations. On the contrary, we have to abandon him. We may not even visit him except for advising and explaining to him the mischief of his ways.
In Islamic Law, the convicted magician should be killed. But this may not be done by individuals. It is only an Islamic court authorized by the political authority of the land that can carry this out after a ruling against him is formally passed by the judge. Meanwhile, Muslims should warn each other not to deal with this magician and to abandon him until he repents.
Source: Islam Today