《资治通鉴·汉纪·汉纪五十五》
春季，黑山军首领张燕与公孙续率兵十万，分三路援救公孙瓒，张燕的援军还未到，公孙瓒秘密派使者送信给公孙续，让他率五千铁骑到北方低洼地区埋伏，点火作为信号，公孙瓒打算自己出城夹击袁绍围城部队。
孝献皇帝戊建安四年春，三月，黑山帅张燕与公孙续率兵十万，三道救之。未至，瓚密使行人赍书告续，使引五千铁骑于北隰之中，起火为应，瓚欲自内出战。
In the spring, the leader of the Black Mountain Army, Zhang Yan, and Gongsun Xu led an army of 100,000 to rescue Gongsun Zan in three ways. Before Zhang Yan's reinforcements arrived, Gongsun Zan secretly sent an envoy to Gongsun Xu, asking him to lead 5,000 iron cavalry to ambush. in the northern lowlands, lighting a fire as a signal, Gongsun Zan planned to lead his own troops out of the city to attack Yuan Shao's siege troops.