《旧唐书·本纪·卷十七》
二十日，诏令各方镇节度观察使请求朝见的，须提前报告，经批准后方可起程前来。二十一日，幽州发生兵变，驱逐原节度使李载义，拥立后院副兵马使杨志诚为留后。
己未，诏方镇节度观察使请入观者，先上表奏闻，候充则任进程，庚申，幽州军乱，逐其帅李载义，立后院副兵马使杨志诚为留后。
On the 20th, an imperial edict was issued ordering all regional pacification commissioner-observers who request to attend the imperial court to report in advance, and they could only set off from their posts after approval. On the 21st, a mutiny took place in You Prefecture, driving out the original Pacification Commissioner Li Zaiyi, and supporting Yang Zhicheng, the deputy commander of the rear troops, as the acting governor.