《北史·列传·卷六十四》
卫玄认为自己年纪已高，上表乞求告老还乡。炀帝派遣内史舍人封德彝驰往京师，告诉他说： 京师是国家的根本，是宗庙园陵的所在地，借助公卧居以镇守之。 
自以年老，上表乞骸骨，帝遣内史舍人封德彝驰喻之曰： 京师国本，宗庙园陵所在，籍公卧以镇之。 
Wei Xuan thought that he was getting old and begged to retire and return to his hometown. Sui Yangdi sent Neishi Sheren Feng Deyi to the capital to tell him: The capital is the foundation of the country and the location of the ancestral temple and mausoleum. With the help of Gong, I can live in peace to guard it.