You shall sleep in a mortar

Explanation

some say Holmus was a seer; others, that those who slept in a mortar (holmos) became prophetic, whence the proverb. And Aristophanes the grammarian says that those who slept in a mortar became prophetic; and that the tripods of Apollo were called "mortars," and Apollo is called by Sophocles "of-the-mortar."