《汉书·传·武五子传》
臣听说孝武帝时派出中郎将苏武出使匈奴，被扣留二十年拒不降敌，回来后仅封为典属国。
臣闻武帝使中郎将苏武使匈奴，见留二十年不降，还亶为典属国。
I heard that during the reign of Emperor Xiaowu, the mid-ranking general Su Wu was sent as an envoy to the Xiongnu, but was detained for twenty years and refused to surrender to the enemy. When he returned, he was given the minor post of Chamberlain for Dependent States.