From Li Yu's 《
虞美人·
春花秋月何时了》 (Southern Tang, ~978), written in captivity after the Song conquered his kingdom:
问君能有几多愁?
恰似一江春水向东流。 The answer — sorrow 'like a river of spring water flowing east' — is among the most famous similes in Chinese literature. Legend says the Song emperor poisoned Li Yu after reading this poem.