《北史·列传·卷二十二》
高闾说 ：奸佞的人装出很有智谋的样子欺骗别人和办事，忠贞的人出于内心符合正道行事，这就像美玉和石头，可以清楚地区分出来。 
闾曰： 佞者饰知以行事，忠者发心以附道，譬如玉石，皦然可知。 
Gao Lu said: The treacherous people pretend to be very resourceful to deceive others and do things, while the loyal people act in accordance with the right path from the heart, which is like jade and stone, and can be clearly distinguished.