From Qu Yuan's Warring-States-era long poem
《离骚》:
路漫漫其修远兮,吾将上下而求索 - 'The road stretches on, long and far; I shall seek up and down without end.'
兮 is a Chu-ci filler particle carrying the rhythm. The couplet is one of the most quoted lines in all classical Chinese literature and is Qu Yuan's signature declaration of unwearied inquiry.