From
李之仪《
卜算子·
我住长江头》(Li Zhiyi, Northern Song):
我住长江头,
君住长江尾。
日日思君不见君,
共饮长江水 (I live at the Yangtze's head, you live at its tail. Day by day I think of you yet never see you — but we drink the same river's water). A famously tender, simple love ci, often set to music and quoted in long-distance-love contexts.