Chapter 6, Verse 34 - Sun Tzu

The five elements (water, fire, wood, metal, earth) are not always equally predominant; the four seasons make way for each other in turn. There are short days and long; the moon has its periods of waning and waxing.
~ from The Art of War, Giles translation ~

Go here to read the introductory post to the verses of The Art of War.