《资治通鉴·汉纪·汉纪四十一》
怀县县令虞诩向任尚建议道： 依据兵法，弱的不去进攻强的，走的不去追赶飞的，这是自然之势。
怀令虞诩说尚曰： 兵法：弱不攻强，走不逐飞，自然之势也。
Yu Xu, the magistrate of Huaixian County, advised Ren Shang: According to military strategy, the weak should not attack the strong, and foot soldiers should not pursue mounted ones. This is how things naturally are.