Does the one who goes to a fortune teller and asks him about something become a kaafir?

There is no contradiction between the two hadeeth. What is meant by the hadeeth “ Whoever goes to a soothsayer and believes what he says has disbelieved in that which was revealed to Muhammad” is that the one who asks a soothsayer a question, believing that he tells the truth and that he knows the unseen, has committed an act of kufr, because he has gone against the Qur’aan in which Allaah says (interpretation of the meaning): “Say: “None in the heavens and the earth knows the Ghaib (Unseen) except Allaah” [al-Naml 27:65]. As for the second hadeeth, “Whoever goes to a fortune teller and asks him about something and believes him, his prayers will not be accepted for forty days”, which was narrated by Muslim, it does not contain the words “and believes him”. 

Thus we learn that if a person goes to a fortune teller and asks him anything, his prayer will not be accepted for forty days, and if he believes him, then he has committed an act of kufr. 

And Allaah is the source of strength. May Allaah send blessings and peace on our Prophet Muhammad and his family and companions. End quote. 

Standing Committee for Academic Research and Issuing Fatwas 

Shaykh ‘Abd al-‘Azez ibn baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan