It is transmitted on the authority of Abu Hurairah (RA) that Allah's Messenger (ﷺ) said: The molar tooth of an unbeliever or the canine teeth of an unbeliever will be like Ubud and the thickness of his skin a three night's journey.
Related hadith on this topic
Explanation & Benefits
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary: Benefits and Issues: When the disbelievers reach Hell, Allah ta'ala, by His perfect power, will make every limb and every part of the disbeliever robust and fresh, greatly increasing his size and stature, so that every part of his body may fully experience the punishment. And this is not difficult for Allah: He can cause the real and actual components of the body to swell and enlarge them to such an extent that a molar tooth becomes as large as Mount Uhud, and the thickness of the skin becomes equal to the distance of a three-day journey. And after the skin is burned, He will restore that skin again, just as after the body decays, decomposes, or is burned, He will resurrect that same body and those same components for reckoning. And today, when certain special types of aircraft ascend to great heights, their bodies swell up significantly.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 7185