Why were the People of the Cave terrifying in their sleep, yet not so after they awoke, and how could they say, "We have remained a day or part of a day," despite the changes in human appearance, hair length, and fingernails after all these years?

Allah Almighty did not mention in the Qur’an the reason for the terror inspired by the sight of the Companions of the Cave. Several opinions have been expressed regarding the cause of this terror, among them what Al-Baghawi mentioned: that it was due to the desolation of the place, or because their eyes were open as if they were awake while they were asleep, or due to the abundance of their hair and the length of their nails, or because Allah prevented people from approaching them by instilling terror. It was also said that the reason was the fear of them being robbers.

The opinion that the terror was due to a change in their appearance has been rejected; Ibn Jarir al-Tabari did not mention it, and Al-Shawkani rejected it by stating that they did not find anything strange about their state when they awoke. The author of "Al-Tahrir wa Al-Tanwir" also rejected it, stating that there was nothing in their physical appearance that deviated from the creation of people.

Ibn Kathir mentions that Allah Almighty cast awe and terror upon them, so that no one would approach them until their slumber ended, due to the profound wisdom in that.