Who are the people who believed yet entered Hellfire?

It is narrated in stories that the Jews and the Christians were the ones who each said to the other: "You are not on anything (of truth)," and this is supported by the Almighty's saying: ﴿And the Jews say the Christians are not on anything, and the Christians say the Jews are not on anything, while they recite the Scripture. Thus speak those who know not, like their words. Allah will judge between them on the Day of Resurrection concerning that over which they used to differ.﴾ [Al-Baqarah: 113].

Truthfulness does not cause one to enter Hellfire; rather, it is a cause for entering Paradise, as stated in the Almighty's saying: ﴿Allah will say: "This is the Day when the truthful will benefit from their truthfulness." For them are Gardens beneath which rivers flow, abiding therein forever. Allah is pleased with them, and they are pleased with Him. That is the great attainment.﴾ [Al-Ma'idah: 119]. As for the Jews and Christians, they entered Hellfire due to their disbelief, and the verse condemns them despite their knowledge of what contradicts their statement, as they used to recite the Scripture.