《旧唐书·本纪·卷十二》
二十五日，安西四镇节度使郭昕、北庭都护李元忠加左右仆射职衔。
乙未，安西四镇节度使郭昕、北庭都护李元忠加左右仆射。
On the twenty-fifth day, Guo Xin, the military governor of the four towns of Anxi, and Li Yuanzhong, the imperial protector of Beiting, were granted the title of Left and Right Servant Adjutant.