Asking the Soothsayers and Sorcerers is Unlawful

Question:

My father was mentally ill, and the period of his sickness lengthened, which included going back and forth from the hospital. Some of my relatives told me to go to a woman who knew a cure for mental illnesses. They also said: "Give your name only, and she will tell you what his sickness is and what the appropriate medicine is." Is it lawful for us to go to this woman?

Answer:

This woman and her like, are unlawful to go to, ask, and believe in, because she is of the soothsayers, and sorcerers, who claim the knowledge of the unseen, and use the Jinn to help them in the cures and their claims. It is authentically reported that the Prophet said:
"He who visits a fortuneteller and consults him, no prayer of his would be accepted for forty days".
It is also authentically reported that the Prophet said:
"He who visits a fortuneteller or a seer and believes him, has certainly denied what was revealed to Muhammad SAW.

The traditions in this meaning are many. Your duty is to warn those people who go to them, and not to ask them nor to believe in what they say, and to report them to the authorities, so that they can be punished with what they deserve. For if you do not report them to the authorities, much destruction shall be made, and some weak people may fall to them, by asking and believing them.

The Prophet SAW said:
" If anyone of you sees something evil, he should change it by his hand; if he is not able to do so, then with his tongue; and if he is not able to do this, then with his heart, and this is the weakest of faith".

Indeed reporting them to the authorities is of the means to stop an evil by your hand, and is working together on good deeds.

Source:
Fatawa Islamiyah, Vol. 1 Pages 97-98