Surah Al-Kahf, Verse 104

ٱلَّذِينَ ضَلَّ سَعۡيُهُمۡ فِي ٱلۡحَيَوٰةِ ٱلدُّنۡيَا وَهُمۡ يَحۡسَبُونَ أَنَّهُمۡ يُحۡسِنُونَ صُنۡعًا١٠٤

alladhīna ḍalla saʿyuhum fī l-ḥayati l-dun'yā wahum yaḥsabūna annahum yuḥ'sinūna ṣun'ʿan

[They are] those whose effort is lost in worldly life, while they think that they are doing well in work."