Closing line of
《上邪》 (Shàng Yé, 'Oh Heaven Above'), a Han-dynasty
乐府 (yuefu) love song:
上邪!
我欲与君相知,
长命无绝衰 (Oh heaven! I want to know you, a life without end or decay). The poem stacks impossibilities - when mountains have no peaks, rivers run dry, winter thunders roar, summer rains snow, heaven and earth merge - only then would the speaker dare to leave. The canonical 'list of impossibilities' love oath in Chinese.