Responsa sobre Josué 9:20

One should not insist that the story of Rahab is different because she benefitted Israel greatly with her kindness toward the two angelic spies, through which all the pathways of the fate of the city of Jericho were revealed; and had they not upheld the oath, they would have replaced good with evil, and there is no worse trait than ingratitude. For the Gibeonites are a counterexample. They deceitfully have to the leaders of the people, swore to them, and made a treaty with them. Then it became clear to all that the Gibeonites acted with deceit. Yet the Israelites did not kill them, for the leaders of the people had sworn to them. Scripture states explicitly on this: “This is what we will do to them: We will spare their lives, so that there may be no wrath against us because of the oath that we swore to them” (Joshua 9:20). This is irrefutable proof that a Jewish man may not swear falsely to any man on this earth, regardless of nation or language. There is no dispensation for this whatsoever. Even if he was tricked and duped into swearing, there is no excuse in the world for swearing falsely.