《后汉书·列传·郑范陈贾张列传》
侍御史杜林先与郑兴同住在陇右，杜林就推荐郑兴道： 我看到河南郑兴，坚守正义，喜好诗书，知识渊博，思想坚定，有公孙侨、观射父的德行，应该留在皇上的身边，掌握国家的机密。
侍御史杜林先与兴同寓陇右，乃荐之曰： 窃见河南郑兴，执义坚固，敦悦《诗》、《书》，好古博物，见疑不惑，有公孙侨、观射父之德，宜侍帷幄，典职机密。
The censor Du Lin and Zheng Xing used to live in Longyou, Du Lin recommended Zheng Xing: I saw Zheng Xing from Henan. He is committed to justice, loves poetry and books, has extensive knowledge, and is very determined. He has the virtues of Gongsun Qiao and Guan Shefu. He should stay by the emperor's side and be in charge of the country's secrets.