《贞观政要·卷七·论礼乐》
后汉，郑仲虞抚养寡居的嫂子和她的儿子，待她的礼节和情义都很笃厚。晋时，颜弘都的嫂子双目失明，需要服用蛇胆，他千方百计弄到蛇胆，终于使嫂子重见光明。后汉将军马援对嫂子极为尊重，不戴帽子就不敢进屋拜见嫂子。《礼记》记载：孔子之孙孔伋在嫂子的灵位前痛哭。这些都是亲身实践礼义规范，极其仁义孝敬的人。能够深明其中大义的，难道不是先知先觉者吗？
郑仲虞则恩礼甚笃，颜弘都则竭诚致感，马援则见之必冠，孔伋则哭之为位，此盖并躬践教义，仁深孝友，察其所行之旨，岂非先觉者欤？
In the Eastern Han Dynasty, Zheng Zhongyu raised his widowed sister-in-law and her son, and his courtesies and affection towards her were very sincere. During the Jin Dynasty, Yan Hongdu's sister-in-law was blind in both eyes and needed to take snake gall. He went to great lengths to obtain snake gall, and finally restored his sister-in-law's sight. The Eastern Han general Ma Yuan was extremely respectful towards his sister-in-law, and would not dare to enter her house to pay his respects without wearing a hat. The Book of Rites records that Confucius's grandson, Kong Ji, wept bitterly before his sister-in-law's spirit tablet. These were all people who put the norms of courtesy and righteousness into practice, and who were extremely benevolent and filial. Could it be that those who are deeply enlightened to the great principles contained therein are not the first to know and understand?