In summer 621, the Tang and Xia forces, commanded by Li Shimin and Dou respectively, engaged at the Battle of Hulao. During the early stages of the battle, Wang Shichong's nephew Wang Wan (王琬) the Prince of Dai, whom Wang Shichong had sent to Xia to request aid, was on the battlefield showing off his handsome horse. Li Shimin made the comment, "What an impressive horse!" Yuchi requested that he be allowed to capture it for Li Shimin, but Li Shimin disallowed it, stating, "How can I lose a great warrior for a horse?" Yuchi did not relent, however, and he took Gao Zengsheng (高甑生) and Liang Jianfang (梁建方) with him; the three of them made a surprise attack into the Xia frontline and seized Wang Wan, capturing him back along with his horse. Later, in the main engagement, Li Shimin defeated and captured Dou, and Wang Shichong, distressed, surrendered. Zheng and Xia territory were seized by Tang.