Tengrism is based on personal relationship with the gods and spirits and personal experiences, which cannot be fixiated in writings; thus there can be no prophet, holy scripture, place of worship, clergy, dogma, rite and prayers. In contrast, Islam is based on a written corpus. Doctrines and religious law derive from the Quran and are explained by hadith. In this regard, both belief systems are fundamentally distinct. Turks usually encountered and assimilated their beliefs to Islam via Sufism. Turks probably identified Dervishes as something akin to shamans. First contact between shamanistic Turks and Islam took place during the Battle of Talas against the Chinese Tang dynasty. Turkic Tengrism further influenced parts of Sufism and Folk Islam, especially Alevism with Bektashi Order. Many shamanistic beliefs were considered as genuinely Islamic by many average Muslims and are still prevalent today.