“Surely, Allah does not wrong even to the measure of a particle, And if it be a good deed, He multiplies it and gives a great reward out of His Own pleasure.” [4:40]
That is, Allah Almighty does not allow the reward of good deeds from anyone be reduced in any manner or quantity whatsoever. In fact, He adds extra rewards, in multiples, in special Divine favours, and the life of Akhirah will witness this supreme mercy of the Lord.
With Allah, the least human measure of thawab or reward is that one good deed gets recorded as ten. Then, this does not stop at that; through sheer mercy and grace, Allah bestows manifold increase into this treasure of good deeds. Some hadith narrations tell us that there are deeds the reward for which rises as high as two million times.
The truth of the matter is that Allah is al-Karim, the most-noble, the most-generous – He Himself, in His limitless mercy and grace, so increases the quantum of his blessing on His servants that it simply cannot be counted or measured in our human terms.
The extents of His generosity and the dimensions of His very Being are beyond human concep¬tualization – who can dare calculate the incalculable
Incidentally, the word, ذَرَّةٍ : dharrah” appearing in this verse has been translated here as ‘particle’ following the generally recognized meaning it carries.
However, some commentators have pointed out that ‘dharrah’ is the name of the smallest kind of red ant which the people of Arabia used to cite as an example of something very light and insignificantly small.
[Tafseer Ma’ariful Qur’an Surah 4 – An-Nisaa – Ayah 40]