Chapter 2, Part 11 - Chuang Tzu

The Penumbra asked the Shadow, saying, 'Formerly you were walking on, and now you have stopped; formerly you were sitting, and now you have risen up:-- how is it that you are so without stability?' The Shadow replied, 'I wait for the movements of something else to do what I do, and that something else on which I wait waits further on another to do as it does. My waiting,-- is it for the scales of a snake, or the wings of a cicada? How should I know why I do one thing, or do not do another?

'Formerly, I, Kwang Kâu, dreamt that I was a butterfly, a butterfly flying about, feeling that it was enjoying itself. I did not know that it was Kâu. Suddenly I awoke, and was myself again, the veritable Kâu. I did not know whether it had formerly been Kâu dreaming that he was a butterfly, or it was now a butterfly dreaming that it was Kâu. But between Kâu and a butterfly there must be a difference. This is a case of what is called the Transformation of Things.'
~ James Legge translation via Stephen R. McIntyre ~

Go here to read the introductory post to the chapters of the Book of Chuang Tzu.