櫛風沐雨

From Zhuangzi:

禹親自操橐耜而九雜天下之川。腓無胈，脛無毛，沐甚雨，櫛疾風，置萬國。禹，大聖也，而形勞天下也如此。 [Traditional Chinese poetry, trad.]

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禹亲自操橐耜而九杂天下之川。腓无胈，胫无毛，沐甚雨，栉疾风，置万国。禹，大圣也，而形劳天下也如此。 [Traditional Chinese poetry, simp.]

From: Zhuangzi, circa 3^rd – 2^nd centuries BCE

Yǔ qīnzì cāo tuó sì ér jiǔ zá tiānxià zhī chuān. Féi wú bá, jìng wú máo, mù shèn yǔ, zhì jífēng, zhì wànguó. Yǔ, dàshèng yě, ér xíng láo tiānxià yě rúcǐ. [Pinyin]

Yu worked with his spade and basket in removing the sludge himself, and eventually diverted the floods into the major rivers. In doing so, he spared no pains and went from place to place in spite of devastating storms of wind and rain to help the stricken people settle down. He walked so much that his shanks were reduced to skin and bones, fine hair on them rubbed away. Yu was a great sage and yet was so much concerned about the common people.

Note that 沐 (mù) originally meant ‘to wash one's hair’, especially here as quoted above, which can be proven by 櫛／栉 (zhì, “to comb one's hair”).

櫛風沐雨

1. to travel and work despite harsh conditions; to work very hard

櫛(しっ)風(ぷう)沐(もく)雨(う) • (shippūmokū) 

1. (idiomatic) to work out in the wind and rain