O You who believe! Show integrity for the sake of Allah, bearing witness with justice. Do not let hatred for a people incite you into not being just. Be just. That is closer to piety. Have fear [and awareness] of Allah. Allah is aware of what you do. (Surat al-Ma'ida, 5:8)
Allah is the most just judge. As His order encompasses the universe, He will show His justice to His servants both in this world and beyond. All the acts of Allah, Who is All-Seeing, All-Knowing, and All-Aware, are for a divine purpose and are just.
Allah will judge all of each person's deeds according to His justice. Allah informs us that those who engage in violence will be punished and that even a single good word will be rewarded. He will manifest His infinite justice in the Hereafter.
The difficulties that unbelievers make for Prophets and believers, as well as their slanderous accusations and sins, will not remain unanswered. All of these difficulties, which raise believers' ranks in Paradise , lead unbelievers to the lowest level of the Fire. On the Day of Judgment, Allah will set up the Just Balance, and no soul will be wronged in any way. Allah will call them to account by ending the time that He has granted them. Given that Allah, the All-Knowing, keeps His promise, all people will see the consequences of their wrong actions in the Hereafter. Thus, unbelievers will be punished severely, while those who remained true to Allah will be rewarded most bountifully. In one verse, Allah states the following:
Those who pledge their allegiance to you [the Prophet] pledge allegiance to Allah. Allah's hand is over their hands. He who breaks his pledge only breaks it against himself. But as for him who fulfils the contract he has made with Allah, We will pay him an immense reward. (Surat al-Fath, 48:10)
There is an important point to consider here: While pondering over His justice, do not compare it with the human concept of justice, for a faithless person, while passing judgment, may well comply with his whims and desires, remain under the influence of his feelings, or forget what has been done. Most importantly, one never knows what is in the other party's mind. But Allah, Who never errs or forgets, has assigned angels for every person in order to observe and record each of their acts and thoughts. In brief, Allah holds each person's soul in His hand. The Qur'an also reveals that our Lord, Who gives the best judgment, is infinitely just:
On the Day We summon every people with their records, those who are given their Book in their right hand will read their Book and will not be wronged by even the smallest speck. (Surat al-Isra', 17:71)
In the Hereafter, Allah will pay back all of the wrong doing and plots hatched against believers. In this life, He may grant the unbelievers many blessings (e.g., wealth and possessions), yet these will only lead them to more evil. In the Qur'an, Allah states that believers must not be attracted to such blessings, for when compared with what awaits them in the Hereafter, the benefits of this short life are insignificant, especially when the infinite punishment of Hell awaits unbelievers.
In the Hereafter, each person's real abode, every soul will find itself confronted with all of its good deeds. Allah will manifest His justice in Hell and Paradise for all eternity. Ultimately, Allah will separate those who believe in Him from those who do not.
Say: “Our Lord will bring us all together and then will judge between us with the truth. He is the Just Decider, the All-Knowing.” (Surah Saba, 34:26)
Allah commands believers to be just as follows:
Allah does not forbid you from being good to those who have not fought you in the religion or driven you from your homes, or from being just toward them. Allah loves those who are just. (Surat al-Mumtahana, 60:8)
Allah commands you to return to their owners the things you hold on trust and, when you judge between people, to judge with justice. How excellent is what Allah exhorts you to do! Allah is All-Hearing, All-Seeing. (Surat an-Nisa', 4:58)
They are people who listen to lies and consume ill-gotten gains. If they come to you, you can either judge between them or turn away from them. If you turn away from them, they cannot harm you in any way. But if you do judge, judge between them justly. Allah loves the just. (Surat al-Ma'ida, 5:42)