Hypocrasie Of Ascetics

Sufi texts tell many stories about people whose hypocrisy was revealed, and they were put to shame.
A famous example is this: A man ostentatiously prayed the whole night through in a mosque he had entered at dusk and where he had heard a sound that seemed to indicate the presence of a human being. But when the call for morning prayer was heard, he discovered that his companion in the mosque was a dog, thus rendering all his prayers invalid and himself impure.

Mystical Dimensions of Islam