Surah Al-Kahf, ayah 104

ٱلَّذِينَ ضَلَّ سَعۡيُهُمۡ فِي ٱلۡحَيَوٰةِ ٱلدُّنۡيَا وَهُمۡ يَحۡسَبُونَ أَنَّهُمۡ يُحۡسِنُونَ صُنۡعًا ١٠٤

Alladhīna dalla sa'yuhum fil-hayawātid-dunyā wahum yahsabūna annahum yuhsinūna sun'ā

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