《后汉书·列传·南匈奴列传》
南北之间仇恨已深，就相互窥伺对方的空隙，引弓举戈，侦察对方动静，像云一样聚集，又像乌一样四散，相互进兵迅速攻击，弄到攻陷溃散重创死伤的地步，没有一年能够安定，但汉的边境地区都安然无事了。
仇衅既深，互同便隙，控弦抗戈，觇望风尘，云屯鸟散，更相驰突，至于陷溃创伤者，靡岁或宁，而汉之塞地晏然矣。
The hatred between the north and south had become very deep, so they spied on each other for opportunities, drew bows and raised weapons, observed each other's movements, gathered like clouds, and dispersed like crows, advanced and attacked each other quickly, leading to capture, rout, severe injury, and death, and not a year could pass peacefully, but the Han border regions were all safe and sound.