《汉书·传·盖诸葛刘郑孙毋将何传》
每次看到他拖着生牛皮鞋，皇上都笑着说： 我能够听得出郑尚书的脚步声。 
每见曳革履，上笑曰： 我识郑尚书履声。 
Every time he heard him dragging his unprocessed leather shoes, the emperor laughed and said: I can tell if that's Secretary of State Zheng by the sound of his footsteps.