Surah 18. Al-Kahf, Ayah 11

I.e., God caused them to remain cut off - physically or metaphorically - from the sounds and the bustle of the outside world. The classical commentators take the above phrase to mean that God "veiled their ears with sleep".

 lit., We cast a cover of ˹deep˺ sleep over their ears.

Drew (a veil) over their ears: i.e., sealed their ears, so that they heard nothing. As they were in the Cave they saw nothing. So they were completely cut off from the outer world. It was as if they had died, with their knowledge and ideas remaining at the point of time when they had entered the Cave. It is as if a watch stops at the exact moment of some accident, and any one taking it up afterwards can precisely fix the time of the accident.