《淮南子·修务训》
曾听说过古书上这样说： 神农憔悴，尧帝清瘦，舜帝脏黑，而禹王手足长茧。 
盖闻传书曰：神农憔悴，尧瘦臞，舜霉黑，禹胼胝。
I have heard it said in ancient books that Shennong was emaciated, Yao was thin, Shun was swarthy, and Yu had calluses on his hands and feet.