Quran

This story proves that whoever flees persecution for the sake of his religion, Allah will protect him from that; whoever strives to maintain his well-being, Allah will grant him that; whoever seeks refuge with Allah, Allah will grant him refuge and cause him to be a means of guidance for others; whoever puts up with humiliation for Allah's sake, seeking His pleasure, the ultimate consequences will be high status for him that will be achieved in a manner that he does not expect. Al-Saadi: 473.
Question: List three useful lessons from the story of the people of the cave.

Building mosques at grave sites and praying at them is prohibited because that is a pretense for worshiping the dead, or similar to the actions of some who worship their righteous dead people. Ibn Ashur: 15/290.
Question: Building Mosques at graves sites is prohibited. Why?

This indicates that the best thing to do in matters like this is to refer knowledge to Allah, because there is no need to indulge in discussing such matters without knowledge. If we are given knowledge of a matter, then we may talk about it; otherwise, we should refrain. Ibn Kathir: 3/77.
Question: When a student of knowledge is questioned about unknown issues to him, what is the best thing for him to do?

This proves that it is not allowed to seek Fatwas from someone who is not fit to issue Fatwas, either because he does not have sufficient knowledge concerning the issue in question, or because he is careless in his talk and may give any answer. This verse also indicates that it may be forbidden to ask a person about some things and not other things, so he may be asked about that of which he has knowledge, but not other matters, because Allah did not forbid us to ask them questions in all cases; rather, He only forbade us to ask them about the story of the people of the Cave and similar matters. Al-Saadi: 474.
Question: Mention some of the issues related to Fatwa, which are derived from this verse?

Meaning: If you intend to do something in the future, do not say, "I will do this tomorrow" unless you say, "If Allah wills." Al-Baghawi: 3/23.
Question: What is the Quranic guidance to what must one say if he wants to do something in the future?

This is guidance to anyone who forgets something in his speech. It is important to remember Allah, as forgetfulness comes from the devil, and the remembrance of Allah drives away the devil, so when the devil is gone, forgetfulness is eliminated. The remembrance of Allah is a cause for remembering. Ibn Kathir: 3/78.
Question: What is the link between remembering Allah and ridding forgetfulness?

A protector (an ally) is one whom you have a reason on which an alliance between you and him is based. Faith is the reason for which the believers are allies of their Lord through obedience, and He is their ally by rewarding, empowering and helping them. Al-Shanqiti: 3/257.
Question: Allah is the ally of the believers, and they are allies of Him. Explain.