Injustice is forbidden
87) Narrated Abfl-Dhar : The Prophet said that Allah said: 0 My slaves! I have forbidden injustice for Myself, so it is forbidden amongst you. So, do not be unjust to each other. 0 My slave! All of you are liable to go astray except the one whom I guide on the right path. So (always) seek guidance from Me, I will guide you. o My slave! All of you are hungry except the one whom I feed. So ask Me for food. I shall feed you. 0 My slave! All of you are naked except the one whom I make wear. So ask Me to make you wear and I shall make you wear. 0 My slave! You commit mistakes (sins) by day and night; and I forgive all the sins. So ask Me forgiveness, I shall forgive you (your sins). 0 My slaves! You will not attain harming Me so as to harm Me, and you will not attain benefiting Me so as to benefit Me. 0 My slaves! Were the first of you and the last of you, the human being of you and the jinn of you to be as pious as the most pious heart of anyone of you, that would not increase My kingdom anything. 0 My slaves! Were the first of you and the last of you, the human of you and the jinn of you to be as wicked as the most wicked heart of anyone of you, that would not decrease My kingdom anything. 0 My slaves! Were the first of you, the last of you, the human of you and the jinn of you to rise up in any place and make a request to Me and I have to give every one what he requested, that would not decrease what I have, anything more than a needle decreases the sea if it is put into it. 0 My slaves! Rather it is but your deeds which I will reckon for you, and then recompense for. So let, who finds good, praise Allah and let, who finds other than that, blame no one but himself.
(This Hadfth is sound and reported by Muslim).
Injustice is one of the most bad qualities most widely practised among men since the dawn of history. Allah made it Haram (unacceptable) and whoever practises injustice cannot be a good Muslim. Allah Who is All-Judicious and AllJust wants us all, to practise every justice among ourselves.