Quran 20:124- Real Happiness Belong To Believers?
This is about intellectual satisfaction which comes with conscious belief in God and the hereafter which makes this world meaningful otherwise it is futile, bleak and purposeless. So, no matter how happy one is, the intellectual void alwasy keeps dissatisfied. The atheist confess that the world without God is bleak but accoring to them this is what they found and this is very disturbing indeed.