Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) says that he heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever goes to a soothsayer and asks him about something, the door of repentance is closed to him for forty nights; and if he believes what he says, he has disbelieved."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18389