I saw the Messenger of Allah ﷺ laugh until his molars became visible. The hadith comes with a long narrative about the story of the last person to leave the Hellfire, and it will appear in its proper place.
لقد رأيت رسول الله ﷺ ضحك حتى بدت نواجذه. والحديث بسياق طويل في قصة آخر أهل النار خروجا منها ويأتي في موضعه.
Muslim narrated it in the Book of Faith (1:314, 190), from Muhammad bin Abdullah bin Numayr, who said, my father narrated to us, Amash narrated to us, from Marur bin Suwayd, from Abu Dharr, who said, then he mentioned it.Nawajidh is the plural of najidh, which is the tooth located between the molar and the canine.