اَلَّذِيْنَ ضَلَّ سَعْيُهُمْ فِى الْحَيٰوةِ الدُّنْيَا وَهُمْ يَحْسَبُوْنَ اَنَّهُمْ يُحْسِنُوْنَ صُنْعًا ( الكهف: ١٠٤ )
Allazeena dalla sa'yuhum fil hayaatid dunyaa wa hum yahsaboona annahum yuhsinoona sun'aa (al-Kahf 18:104)
[They are] those whose effort is lost in worldly life, while they think that they are doing well in work." (Al-Kahf  : 104)
1 Mufti Taqi Usmani
Those are the ones whose effort in the worldly life has gone in vain, while they think they are doing well.