Say, ˹O Prophet,˺ “Shall we inform you of who will lose the most deeds?˹They are˺ those whose efforts are in vain in this worldly life, while they think they are doing good!”It is they who reject the signs of their Lord and their meeting with Him, rendering their deeds void, so We will not give their deeds any weight on Judgment Day.Quran 18:103~105 (Surah al-Kahf)
Al-Kahf (Arabic: الكهف, al-kahf; meaning: The Cave) is the 18th chapter (sūrah) of the Quran with 110 verses (āyāt).
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قُلۡ هَلۡ نُنَبِّئُكُم بِٱلۡأَخۡسَرِینَ أَعۡمَـٰلًا

ٱلَّذِینَ ضَلَّ سَعۡیُهُمۡ فِی ٱلۡحَیَوٰةِ ٱلدُّنۡیَا وَهُمۡ یَحۡسَبُونَ 
أَنَّهُمۡ یُحۡسِنُونَ صُنۡعًا

أُو۟لَـٰٓئِكَ ٱلَّذِينَ كَفَرُوا۟ بِـَٔايَـٰتِ رَبِّهِمْ وَلِقَآئِهِۦ فَحَبِطَتْ أَعْمَـٰلُهُمْ فَلَا نُقِيمُ لَهُمْ يَوْمَ ٱلْقِيَـٰمَةِ وَزْنًۭا
There is a hadith in Sahih Muslim that states that Muhammad said (Concerning The False Messiah, Al-Masih ad-Dajjal):
“He who amongst you would survive to see him should recite over him the opening verses of Sura Kahf”
— Sahih Muslim, Book 41, Number 7015
کہہ دو کہ ہم تمہیں بتائیں جو عملوں کے لحاظ سے بڑے نقصان میں ہیں 

وہ لوگ جن کی سعی دنیا کی زندگی میں برباد ہوگئی۔ اور وہ یہ سمجھے ہوئے ہیں 
کہ اچھے کام کر رہے ہیں 

یہ وہ لوگ ہیں جنہوں نے اپنے پروردگار کی آیتوں اور اس کے سامنے جانے سے انکار کیا تو ان کے اعمال ضائع ہوگئے 
اور ہم قیامت کے دن ان کے لئے کچھ بھی وزن قائم نہیں کریں گے
This Surah was sent down in answer to three questions which the polytheists of Makkah in consultation with the People of the Book (the Jews and the Christians) put to the Prophet. These were:
Who were ‘The Sleepers of the Cave?’
What is the real story of Khidr?
What do you know about Dhul-Qarnain?
These three questions and their stories related to the history of the Christians and the Jews and were unknown in the Arabian Peninsula (Hijaz), so they were being used to test the divine knowledge revealed to the Prophet. However, God informed the Prophet of the complete answer to these questions and also employed the stories in the conflict between Islam and unbelief.
The questioners were told that the ‘Sleepers of the Cave’ believed in the same doctrine of Monotheism (Tawhid) which was being put forward in the Qur’an and that their condition was similar to that of the persecuted Muslims of Makkah. Also, the persecutors of the Sleepers of the Cave behaved in the same way as the disbelievers of Quraysh towards the Muslims. This particular story was a warning to the chiefs of Makkah, who were persecuting the small newly formed Muslim community. Additionally, the Prophet was instructed not to compromise with the persecutors nor consider the chiefs to be more important than his own followers. Likewise, the chiefs too were admonished and informed not to be distracted by the temporary life of this world but seek the eternal life of the hereafter.