《史记·七十列传·魏公子列传》
秦国又多次实行反间，利用在秦国的魏国间谍，假装不知情地请他们向公子祝贺问是否已经立为魏王了。
秦数使反间，伪贺公子得立为魏王未也。
The Qin state had also repeatedly implemented counter-espionage, utilizing the Wei spies in Qin, and pretending to be unaware of the situation, asking them to convey their congratulations to the prince and ask if he had already been installed as the King of Wei.