It is narrated from Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Any man who goes to a soothsayer and asks him something, repentance is withheld from him for forty nights; and if he believes what the soothsayer says, he has disbelieved in Allah."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18445