Truthfulness is approached here from several angles: the Quran and the Messenger ﷺ confirm what came before them, and none is truer in speech than Allah. The verses mention prophets of perfect truthfulness, genuine truthfulness made of faith and deeds, the reward of the people of truth, the command to be with the truthful, and Mary, daughter of ʿImran, described as truthful.
Verses gathered from a topical index of the Quran, in Mushaf order; every verse is quoted in full.
Allāh - there is no deity except Him. He will surely assemble you for [account on] the Day of Resurrection, about which there is no doubt. And who is more truthful than Allāh in statement.
But the ones who believe and do righteous deeds - We will admit them to gardens beneath which rivers flow, wherein they will abide forever. [It is] the promise of Allāh, [which is] truth, and who is more truthful than Allāh in statement.