Jerusalem Talmud, Nedarim 9:41b/c

And you shall love your neighbor - Rabbi Akiva says, "This is a great principle of the Torah." Ben Azzai says, "'This is the genealogy of Adam' is the great principle of the Torah." Would not then poverty not constitute a new circumstance that would allow for the annulment of a vow? Rabbi Zeira said, "Poverty is common [and therefore one may use it to begin the process of annulling vows]. Like once it happened. A poor man had [a rich man] as a litigant [in a case against him] that would, in the future, come to be judged by Rav. Rav sent a message to [the rich man]. He responded, "Will I come to be judges with that one?! If they bring all the camels of Arabia, they wouldn't be able to pull off the clasps of my storehouses!" [Rav] heard [about the ridiculous thing the rich man said] and said, "How can someone take such an oath on things he has no control over?" Immediately a royal decree went forth stating that he and all his property should be confiscated. He went before Rav and said, "Pray for me, that my life should be saved." He prayed for him and his life was saved. [Translation by Noah Bickart]