Chapter 33, Part 2C - Chuang Tzu

Mo Tzu defends his teachings by saying, "In ancient times, when Yu dammed the flood waters and opened up the courses of the Yangtze and the Yellow River so that they flowed through the lands of the four barbarians and the nine provinces, joining with the three hundred famous rivers, their three thousand tributaries, and the little streams too numerous to count - at that time Yu in person carried the basket and wielded the spade, gathering together and mingling the rivers of the world, till there was no down left on his calves, no hair on his shins; the drenching rains washed his locks, the sharp winds combed them, while he worked to establish the ten thousand states. Yu was a great sage, yet with his own body he labored for the world in such fashion!"

So it is that many of the Mo-ists of later ages dress in skins and coarse cloth, wear wooden clogs or hempen sandals, never resting day or night, driving themselves on to the bitterest exertions. "If we cannot do the same," they say, "then we are not following the way of Yu, and are unworthy to be called Mo-ists!"
~ Burton Watson translation via Terebess Asia Online ~

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