《资治通鉴·唐纪·唐纪六十二》
郑覃的性情清正俭约，陈夷行也性情耿直。所以，杨嗣复等人十分痛恨他俩人。
覃性清俭，夷行亦耿介，故嗣复等深疾之。
Zheng Tan was honest and frugal by nature, and Chen Yixing was also upright by nature. Therefore, Yang Sifufu and others hated them very much.