The Quran mentions them in a few thunderous verses: cursed were the companions of the ditch, the fire full of fuel, when they were sitting beside it, witnessing what they were doing to the believers, and they resented them for nothing except that they believed in Allah (85:4-8). The Prophet ﷺ then told the full story, and it is one of the most extraordinary narratives in the hadith literature.
A king had a sorcerer, who took an apprentice boy. On his route the boy met a monk and found real faith. He began healing the blind and the sick, telling everyone the healer was Allah, not him. The king tortured him, and every execution attempt failed, thrown off a mountain, thrown into the sea, the boy walked back each time. Finally the boy told the king exactly how to kill him: gather the people, tie me to a post, and say “In the name of Allah, the Lord of the boy.” The king did. The boy died. And the entire crowd said, “We believe in the Lord of the boy.” The king dug trenches, lit fires, and burned everyone who refused to recant.