Book 4: 《里仁》 Li Ren (Brotherliness)
《里仁》 Passage 4.7
子曰：「人之過也，各於其黨。觀過，斯知仁矣。」
Legge Translation (1861)
The Master said: "The faults of men are characteristic of the class to which they belong. By observing a man's faults, it may be known that he is virtuous."