"If a person goes to a fortune-teller and asks him about something, his prayer will not be accepted for forty nights.”

Muslim recorded this in his Sahih. It is authentically narrated that he said,

"Whoever goes to a fortune-teller or a soothsayer and believes in what he says, he has then disbelieved in what has been revealed to Muhammed (sallallaahu ‘alaihi-wasallam).” [1]

There are many Ahadith with that meaning. Therefore, it is a must to stop such people and those who visit them. They should not be questioned nor should they be believed. They should be taken to the people in authority in order to receive the punishment they deserve. Allowing them to be present and not taking them to the authorities harms society as a whole. Leaving them would also help them in deceiving the ignorant people, who will ask them questions and believe in them. [2]

The Prophet (sallallaahu ‘alaihi-wasallam) said,

"If anyone of you sees an evil, he must change it with his hand. If he is not able to, then he should do so with his tongue. And if he still not able to, then with his heart and that is the weakest of faith.”

This was recorded by Muslim in his Sahih. There is no doubt that taking them to the authorities, such as the mayor of the city, the people whose job it is to enforce right and eradicate evil, and the courts, is part of the general concept of removing them by one’s tongue. It is also part of helping another in righteousness and piety. May Allah support all the Muslims in that which is best for them and protect them from every evil.

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[1] Recorded by Ahmed. It seems that the correct version in Sahih Muslim is without the words "and believes in what he says.” Allah Knows Best.

[2] The ruling in this question also applies to all of the other forms of predicting the future that have become commonplace in the West, such as astrologers and psychic networks. Muslims must avoid them completely and must not believe in their statements.