Surah Az-Zalzala (The Earthquake ) 99 : 8

Explanatory Note

This atom, or what is similar to it in weight, whether good or bad, will be brought forth and shown to its doer, who will then receive its reward. At that time man does not undervalue any of his actions and deeds, whether good or bad. On the contrary, his conscience will be as sensitive to everything he has done as an accurate scale registering even the weight of an atom favourably or unfavourably. There is nothing parallel or similar to this measure in this world, except the heart of a believer. Such a heart is sensitive to even an atom’s weight of either good or evil.
 
But there are some hearts in this world which are unmoved even by mountains of sin and crime. They remain unaffected while suppressing fountains of goodness which are far firmer than mountains. These hearts are conceited on this earth but on the Day of Judgement they are crushed under their own burdens.