《汉书·传·匈奴传下》
单于说： 孝宣皇帝、孝元皇帝哀怜我们，与我们约定，从长城以南归汉朝天子所有，从长城往北归单于所有。
单于曰： 孝宣、孝元皇帝哀怜，为作约束，自长城以南天子有之，长城以北单于有之。
The Great Chanyu said: "Emperor Xuan and Emperor Yuan pitied us, and made an agreement with us that everything south of the Great Wall would belong to the Son of Heaven of the Han, while everything north of the Great Wall would belong to the Great Chanyu."