To believe in Adl (devine justice) means to believe that God acts in accordance with justice in the system of creation, in legislation and in reward and punishment

God is just beyond all injustices

To perform any act which would be cosidered indecent or oppressive by a sane mind is an imperfection

yet God is perfect

thus he must be just

ref:A manual of Islamic Beliefs and Practice I/Naqvi/p:5