A Chinese folk poem from the Han dynasty, by an unknown author, mentions five impossible events that would cause them to give up their love entirely. 

This poem is also cited by the renowned romance novelist Qiong Yao in her work Princess of Pearl.

Read this poem –

Till mountains crumble

Till rivers run dry

Till thunder rumbles in winter

Till snow falls in summer

And the earth mingles with the sky

Not till then will my love die.