Companions of The Cave supplicated for...

"Do you think that the people of the Cave and the Inscription (the news or the names of the people of the Cave) were a wonder among Our Signs? (Remember) when the young men fled for refuge (from their disbelieving folk) to the Cave, they said: “Our Lord! Bestow on us mercy from Yourself, and facilitate for us our affair in the right way!” Therefore, We covered up their (sense of) hearing (causing them, to go in deep sleep) in the Cave for a number of years. Then We raised them up (from their sleep), that We might test which of the two parties was best at calculating the time period that they had tarried." [18: 9-12]

"Do you think that the people of the Cave and the Inscription (the news or the names of the people of the Cave) were a wonder among Our Signs?" - Meaning: Their affair was not something amazing in relation to Allah’s All-Encompassing Power and Authority Over all affairs, for indeed the creation of the heavens and earth, the alternation of night and day, the subjugation of the sun, moon, the stars and the other mighty signs demonstrates Allah’s All-Encompassing Power. Allah is able to do whatever He wills and nothing (in the heavens or in the earth) escapes Him. Ibn Jurayj reported from Mujahid who stated about the meaning of the above Ayah: You are amazed by the story of the people of the cave! Indeed, there are among the signs of Allah that which is more amazing than that. [Al-Misbahul Muneer Fi Tahdbeeb Tafseer Ibn Katheer] Allah has not ceased showing His slaves signs in the universe and in their ownselves, by way of which truth is distinguished from falsehood, and guidance from misguidance. [Tayseer Al-Kareem Ar-Rahmaan Fi Tafseer Kalaam al-Manaan]

"(Remember) when the young fled to the Cave" - Meaning: Intending to fortify and shield themselves from the Fitna of their people.

"they said: Our Lord! Bestow on us mercy from Yourself" - Meaning: Make us steadfast by way of it, protect us from evil and bestow good upon us. "And facilitate for us our affair in the right way!" - Meaning: Facilitate for us every means that will lead us to the right way and make our religious and worldly affairs upright. So, they hurried away and fled from Fitna (and went) to a place where they can hide. They supplicated to Allah with humility to make their affair easy and did not merely rely upon themselves and others; and due to this, Allah answered their supplication and brought about for them that which they could not expect.

Allah said: "Therefore We covered up their (sense of) hearing in the Cave for a number of years" - Meaning: Allah made them sleep for three hundred and nine years. And by way of this sleep, Allah protected their hearts from confusion (or corruption) and fear, and from (the fitna) of their people; so that they might be a manifest sign (to the people). "Then We raised them up (from their sleep), that We might test which of the two parties was best at calculating the time period that they had tarried" - Meaning: Which of them could calculate the time period they stayed in the cave, just as Allah said: "Likewise, We awakened them (from their long deep sleep) that they might question one another." The knowledge regarding how long they slept in the cave demonstrates precision in calculation, knowledge of Allah’s All-Encompassing Power, Wisdom and Mercy. And had they continued to sleep; nothing would have been known regarding their story. [Tayseer Al-Kareem Ar-Rahmaan Fi Tafseer Kalaam al-Manaan]

After mentioning the Imaan and guidance bestowed upon them by Allah (i.e. in Ayaat 13 and 14), they then addressed what their people were upon. Their people used to set up rivals unto Allah (in worship), so they detested them and clarified that their (beliefs, acts of worship etc) were not based on certainty; rather they were (a people) upon extreme ignorance and misguidance. Allah said that the young men said: "These our people have taken for worship aliha (gods) other than Him (Allah). Why do they not bring for them a clear authority? And who does more wrong than he who invents a lie against Allah." [18:15]

"Why do they not bring for them a clear authority?" - Meaning: Bring Hujjah (i.e. clear and overwhelming proofs that would show the correctness of what they are upon and the falsehood of their opponents) and Burhaan (i.e. evidences that clarify and distinguish between truth and falsehood from every angle); however they have no way of doing so, rather they only invent a lie against Allah and this is the greatest type of oppression (or transgression). This is why Allah said that the young men said: "And who does more wrong than he who invents a lie against Allah." [Tayseer Al-Kareem Ar-Rahmaan Fi Tafseer Kalaam al-Manaan]