Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "Whoever goes to an arraf (a diviner or soothsayer), his prayer is not accepted for forty days."
Al-Tabarani recorded it in al-Mu'jam al-Awsat, and its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطب / 8484