What is called `mind' is a wondrous power residing in the Self. It causes all thoughts to arise. Apart from thoughts, there is no such thing as mind. Therefore, thought is the nature of mind. Apart from thoughts, there is no independent entity called the world. In deep sleep there are no thoughts, and there is no world. In the states of waking and dream, there are thoughts, and there is a world also.
Just as the spider emits the thread (of the web) out of itself and again withdraws it into itself, likewise the mind projects the world out of itself and again resolves it into itself. When the mind comes out of the Self, the world appears. Therefore, when the world appears (to be real), the Self does not appear and when the Self appears (shines) the world does not appear. When one persistently inquires into the nature of the mind, the mind will end leaving the Self (as the residue). What is referred to as the Self is the Atman.
--Collected Works - Who Am I?