《战国策·燕三·燕太子丹质于秦亡归》
这时候，太子已经预先寻到天下最锋利的匕首，那是从徐夫人手里用一百金才买到的匕首。太子让工匠用毒药水淬染匕首，拿它在人身上试验，只要流出一点儿血，那人就会立刻死去。
于是，太子预求天下之利匕首，得赵人徐夫人之匕首，取之百金，使工以药淬之，以试人，血濡缕，人无不立死者。
By this time, the crown prince had already sought out the world's sharpest dagger in advance, which was a dagger he had bought from Madam Xu for a hundred ounces of gold. The crown prince had the craftsman quench the dagger with poisonous water and tested it on a person, and as long as a little blood flowed out, that person would immediately die.