《史记·三十世家·留侯世家》
再说跟太子一起出征的各位将领，都是曾经同皇上平定天下的猛将，如今让太子统率这些人，这和让羊指挥狼有什么两样，他们决不肯为太子卖力，太子不能建功是必定的了。
且太子所与俱诸将，皆尝与上定天下枭将也，今使太子将之，此无异使羊将狼也，皆不肯为尽力，其无功必矣。
Moreover, the generals who will go with the crown prince on the expedition are all brave men who followed the emperor in pacifying the empire, now you want the crown prince to command these people, isn’t this like letting a sheep command wolves, they will definitely not fight for the crown prince and the crown prince is destined not to achieve anything.