《汉书·传·西域传下》
从前，我的头脑糊涂因军候弘上书说： 匈奴人捆住马的前后蹄，放在长城脚下，骑着马叫喊： 秦人，我给你们分马。 又汉朝使者被匈奴扣留的很久不得归来。所以我就派贰师将军征伐，以增强汉使的威信。
曩者，朕之不明，以军候弘上书言 匈奴缚马前后足，置城下，驰言 秦人，我匄若马  ，又汉使者久留不还，故兴遣贰师将军，欲以为使者威重也。
In the past, my head was confused because a military officer wrote: "The Huns tied the front and hind hooves of horses and placed them under the Great Wall. They rode on their horses and shouted: Qin people, I will give you horses. And Han messenger was detained by the Huns for a long time and could not return. So I sent the second teacher general to conquer, to enhance the prestige of the Han envoy.