Some people asked the Prophet regarding the soothsayers. He said, "They are nothing." They said, "O Allah's Apostle! Some of their talks come true." The Prophet said, "That word which happens to be true is what a Jinn snatches away by stealth (from the Heaven) and pours it in the ears of his friend (the foreteller) with a sound like the cackling of a hen. The soothsayers then mix with that word, one hundred lies."
English reference: Vol. 9, Book 93, Hadith 650
Arabic reference: Book 98, Hadith 7656