《贞观政要·卷五·论公平》
所以谚语说： 若要人不知，除非己莫为；若要人不听见，除非自己不说。 
故谚曰： 欲人不知，莫若不为；欲人不闻，莫若勿言。 
Therefore, the proverb says: If you don't want people to know, unless you don't do it yourself; If you don't want people to hear, unless you don't say it yourself.