These were some Christian young men who had taken shelter in a cave because the king of their time had ordered the killing of all those who refused idol worship (Verses:15,16). Their number, place and date of the happening are not mentioned probably to indicate the insignificance of details which have no moral value. They were kept sleeping for probably 300 solar years which are equivalent to 309 lunar years [one solar year is 10.95 days longer than a lunar year]. During sleep, they were unconscious of time. This incident hints at life after death and being unconscious of time during death (39:42).