《资治通鉴·汉纪·汉纪十》
 匈奴难以制服，不是这一代才如此。侵犯城邑劫掳人畜，这是他们的生业，天性本来就是这样。
 夫匈奴难得而制，非一世也；行盗侵驱，所以为业也，天性固然。
The Xiongnu were difficult to subdue, and this was not only the case in this generation. In invading cities and looting people and animals, this was their livelihood, and their nature was originally like this.