ANSWER:

There is no problem in making Duaa against a sorcerer. However, no one has the ability to know the unseen except Allah azza wa Jal and anyone who claims to know the unseen is a soothsayer and a liar.  If you think you have been afflicted with magic, make ruqyah on water and drink a lot from it until you are cured by the will of Allah. 

You must maintain your daily adhkar of morning and evening, before going to bed, after every fard prayer, while entering the washroom, while going out of the house, before eating etc and this will act as a shield against everything evil with the Mercy of Allah. You will find these duas in a booklet called ‘Hisnul Muslim’ or ‘Fortress of the Muslim.’  

whats the ruling regarding relatives of husband who you confirm are doing black magic on wife and as a results its affecting children and wife. can we make dua against a sahir .or how do we relate to them.