《新唐书·列传·卷一百二十七》
有个叫郑相如的人，从沧州来，以师礼侍奉郑虔，虔未以礼相待，一会儿问他所习何业，郑相如说： 闻孔子说： 继周者百世可知。 我也能知道。 
有郑相如者，自沧州来，师事虔，虔未之礼，间问何所业，相如曰： 闻孔子称 继周者百世可知 ，仆亦能知之。 
A man named Zheng Xiangru came from Cangzhou and paid Zheng Qian respect as a teacher, but Qian did not treat him respectfully. He soon asked him what he studied, and Zheng Xiangru replied, "I heard Confucius say, 'The successor to the Zhou will be known in a hundred generations.' I can also tell."