《资治通鉴·汉纪·汉纪四十七》
杜密曾经担任过北海国的宰相，在一次春季例行巡视中，走到高密县，遇见担任乡啬夫的郑玄，知道郑玄不是平凡的人，就聘请他担任郡职。不久，又选派他到京都洛阳的太学求学，最后终于成为大儒。
密尝为北海相，行春，到高密，见郑玄为乡啬夫，知其异器，即召署郡职，遂遣就学，卒成大儒。
Du Mi once served as the Prime Minister of Beihai Kingdom. During a spring patrol, he went to Gaomi County and met Zheng Xuan, who was a village porter. Knowing that Zheng Xuan was not an ordinary person, he appointed him to a county post. Soon, he sent him to study at the Imperial University in Luoyang, where he eventually became a great Confucian.