《孔子家语·观周》
孔子在周国观览，进入周太祖后稷的庙内。庙堂右边台阶前有铜铸的人像，嘴被封了三层，还在像的背后刻着铭文： 这是古代说话谨慎的人。警戒啊！
孔子观周，遂入太祖后稷之庙，庙堂右阶之前，有金人焉。参缄其口，而铭其背曰： 古之慎言人也，戒之哉！
Confucius studied in Zhou and entered the temple of Houji, the great ancestor of Zhou. In front of the steps on the right side of the temple hall, there was a bronze statue with its mouth sealed with three layers of metal. An inscription was carved on the back of the statue that said: This is the person who spoke cautiously in ancient times. Be warned!