In Sufi epistemology, 'Shirk-e Khafi' (Hidden Polytheism) refers to the subtle act of attributing agency, causation, or power to worldly things rather than to God alone. In Attar's Tale 10 of the Elahi Nameh, Bayazid Bastami is admonished by God for committing this hidden shirk when he suffers a stomach ache and attributes it to having drunk milk. God interprets this statement as a breach of absolute Tawhid (Oneness), because attributing an effect to a secondary cause (the milk) detracts from recognizing God as the sole ultimate cause of all states and conditions. This narrative illustrates the extremely rigorous standard of spiritual purity and absolute reliance on God expected of advanced Sufi seekers.