Al-Kahf 18:104

Allatheena dalla saAAyuhumfee alhayati addunya wahum yahsaboonaannahum yuhsinoona sunAAa

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

Those are the ones whose effort in the worldly life has gone in vain, while they think they are doing well.