Tafsir of Ghafir 40:17

This Day shall every person be recompensed for what he earned. This Day no injustice (shall be done to anybody). Truly, Allah is swift in reckoning. Here Allah tells us of His justice when He judges between His creation; He does not do even a speck of dust's weight of injustice, whether it be for good or for evil. For every good deed He gives a tenfold reward and for every bad deed He gives recompense of one bad deed. Allah says:

ﻻ ظلم اليوم

(This Day no injustice (shall be done to anybody)). It was reported in Sahih Muslim from Abu Dharr, may Allah be pleased with him, that the Messenger of Allah said that Allah said:

يا عبادي إني حرمت الظلم على نفسي وجعلته بينكم محرما فﻼ تظالموا

إلى أن

قال يا عبادي إنما هي أعمالكم أحصيها عليكم ثم أوفيكم إياها فمن وجد خيرا فليحمد الله تبارك وتعالى ومن وجد غير ذلك فﻼ يلومن إﻻ نفسه

"O My servants, I have forbidden injustice for Myself, and made it unlawful for you, so do not commit injustice to one another ...'' up to: "O My servants, these are your deeds, I record them for you then I will recompense you for them. Whoever finds something good, let him give praise to Allah, and whoever finds something other than that, let him blame no one but himself.''

إن الله سريع الحساب

Truly, Allah is swift in reckoning. means, He will bring all His creation to account as if He is bringing just one person to account. This is like the Ayah:

ما خلقكم وﻻ بعثكم إﻻ كنفس وحدة

The creation of you all and the resurrection of you all are only as a single person, (31: 28)

وما أمرنا إﻻ وحدة كلمح بالبصر

And Our commandment is but one as the twinkling of an eye. (54:50)