《贞观政要·卷九·论征伐》
礼部尚书江夏人王道宗跟随唐太宗征伐高丽，唐太宗命王道宗和李为先锋。他们渡过辽水，攻克了盖牟城之后，敌军大举进攻，军中有人建议挖深沟以求保险，等唐太宗到了，再慢慢攻打他们。
礼部尚书江夏王道宗从太宗征高丽，诏道宗与李勣为前锋，及济辽水克盖牟城，逢贼兵大至，军中佥欲深沟保险，待太宗至，徐进。
Wang Daotong, Minister of the Ministry of Rites from Jiangxia, accompanied Emperor Taizong of Tang in his conquest of Goguryeo. Emperor Taizong ordered Wang Daotong and Li to lead the vanguard. They crossed the Liao River and captured Gaimu City. Later, the enemy launched a massive attack. Some people in the army suggested digging a deep ditch for protection and waiting for Emperor Taizong's arrival before attacking the enemy slowly.