'Adl (fairness and justice) is I’tidal (balance), and in balance lies the correction of the heart, just as in zulm (imbalance/oppression) lies its corruption. This is why for every sin that the person has committed he has oppressed his self (zaliman li nafsihi). The opposite of zulm is 'Adl, so this sinful person has not been just to his self rather he has oppressed it. The correction of the heart lies in 'Adl and its corruption lies in zulm. Therefore, when the servant oppresses himself he is the oppressor and oppressed at the same time, likewise when he is just then he is the one who is just and the one upon whom the justice is carried out. The person does an action and he will receive the fruit of this action, be it bitter or sweet.
Allah said: …He has the reward for the (good) that he has earned, and he is punished for the (evil) which he has earned… [Surah al-Baqarah (2) : 286]
'Aml (actions) have an effect upon the heart, either of benefit, harm, or correction, before they effect the external body. The good and pure actions constitute justice for the soul whereas bad actions oppress the soul.
Allah the Most High, said, Whoever does righteous deeds it is for the (benefit of) himself, and whosoever does evil, it is against his own self. [Surah Fussilat : 46]
If you do good, you do good for your own selves, and if you do evil, you do it against yourselves. [Surah al-Isra : 7]