《资治通鉴·唐纪·唐纪三十九》
剩下留守边镇的部队势单力薄，吐蕃军队便逐渐地将他们蚕食。数年时间，西北地区数十州相继沦陷，自凤翔以西，州以北，均为吐蕃军队所占领。当初，仆固怀恩奉肃宗诏令在太原与回纥可汗会晤，因为回纥可汗是仆固怀恩的女婿，河东节度使辛云京害怕他们合谋袭击军府，所以关闭城门，守备森严，也不去犒劳他们的部队。
初，仆固怀恩受诏与回纥可汗相见于太原；河东节度使辛云京以可汗乃怀恩婿，恐其合谋袭军府，闭城自守，亦不犒师。
The remaining troops guarding the border towns were weak and vulnerable, so the Tibetan army gradually whittled them away. Over a period of several years, dozens of prefectures in the northwest fell in succession, and all the land west of Fengxiang and north of the states was occupied by the Tibetan army. Earlier, pursuant to an imperial decree issued by Emperor Suzong, Pugu Huaien had met with the Uyghur khan in Taiyuan because the Uyghur khan was Pugu Huaien's son-in-law. The commissioner for the Hedong Circuit, Xin Yunqing, was afraid that they would collude to attack the military headquarters, so he closed the city gates, guarded them heavily, and did not go to welcome their troops.