Hazrat Mahdi (as) will rule with equity and justice

The lord of believers (saas) says: "... THE IMAM [HAZRAT MAHDI (AS)] WILL BETTER KNOW WHAT IS TRUE AND WHAT IS FALSE. HE WILL DO AWAY WITH FALSE LAWS. HE [HAZRAT MAHDI (AS)] WILL PREVENT DANGERS AND NEUTRALIZE YOUR UNJUST RULERS AND WILL CLEANSE THE WORLD OF THOSE WHO ARE NOT HONEST. HE WILL ACT WITH EQUITY AND BUILD A MERCIFUL SCALE OF JUSTICE AMONG YOU... If you wait, you will be rewarded and YOU WILL REALIZE THAT IS DEFINITELY THE ONE WHO WILL SALVAGE YOUR RIGHTS and take revenge for the injustice inflicted upon you. I swear by the name of Allah, that Allah is with the truly devout and those who do good.”

Kitab al Ghaybat, [Bihar al-Anwar, Vol. 51], Ansariyan Pubcations, collected by: Muhammad Baqr al-Majlisi, Iran-Qum, 2003, p. 182.