《资治通鉴·汉纪·汉纪二十一》
这是理由之九。如果撤销边防军队，废除边境上用于伺望侦察的土堡，匈奴单于必定自认为保塞守边，对汉朝有大恩德，将不断请求赏赐，如果稍有失望，那么后果就难以推测。
如罢戍卒，省候望，单于自以保塞守御，必深德汉，请求无已；小失其意，则不可测。
This is the ninth reason. If the border guards are revoked, the fortresses used for observation and reconnaissance on the border will be abolished, and the Huns Shanyu will definitely believe that he is defending the border and doing great favors to the Han Dynasty. He will continue to ask for rewards. If he is slightly disappointed, The consequences are hard to predict.