《资治通鉴·唐纪·唐纪六十二》
宰相李德裕认为： 那颉啜屯驻在燕山以北，乌介可汗恐怕他和奚族、契丹族同谋，在自己返回沙漠以南时半路袭击，所以不敢远离边塞。
李德裕以为 那颉啜屯于山北，乌介恐其与奚、契丹连谋邀遮，故不敢远离塞下。
Prime Minister Li Deyu believed that: Na Jie Chu stationed north of Yan Shan, and the Khan of the Uyghurs feared that he would conspire with the Xi tribe and Qidan tribe, and attack while he was returning south of the desert, so he dared not stray too far from the border fortress.