《金史·列传·卷五十一》
于是，白撒便进攻卫州。当军队到达城下时，用黄伞御旗招降城里人，他们却不肯投降。
白撒遂攻卫州，兵至城下，御旗黄伞招之不下。
Therefore, Baisa attacked Weizhou. When the army reached the foot of the city, he used a yellow umbrella as a royal standard to call upon the townspeople to surrender, but they refused.