In a certain city there were young men who believed in their Lord. Allah increased them in guidance and strengthened their hearts. They stood up and said: our Lord is the Lord of the heavens and the earth; we will never call on anyone besides Him.
While their people worshipped others besides Allah, they took refuge in a cave to save their faith. As they entered they prayed:
Allah made them sleep. When the sun rose it inclined away from the cave to the right, and when it set it passed them by on the left, while they lay in the open space within. You would have thought them awake, though they slept; Allah turned them over to the right and the left. And their dog lay with its forelegs stretched out at the entrance.
The Quran tells us they stayed in the cave three hundred years, and nine more. On waking they thought they had slept a day or part of a day. They sent one of them to the city with their coins to bring the purest food, carefully, so that no one would notice.
In this way Allah made their story known, so that people would know Allah's promise is true and there is no doubt about the Hour.
People guess how many they were — three, five or seven. The Quran says: my Lord knows best their number; do not argue about it much.