[4:135] O you who believe, be upright in justice; witnesses for God, even though it be against yourselves; or parents and kinsmen, whether the person be rich or poor; God is closer to the two. So do not follow any whim, lest you swerve, for if you twist, or refrain, surely God is ever aware of what you do.
'Justice' (qis?) is being fair and equitable (ʿadl). Being upright through God in fairness is fulfilling His rights against you and seeking to have His rights fulfilled among everyone with whom you have business. The way to make that happen is either through an exhortation to act kindly or a rebuke concerning something despicable or admonitory advice or direction to a legal issue or guidance to a duty. Whoever has a duty (ḥaqq) remaining owed to God, the purest part of realization (taḥqīq) will not touch his innermost self. The root of religion is to prefer the rightful due of the Real (ḥaqq al-ḥaqq) over the right of created beings. Whoever prefers anyone to God, whether it be a father, mother, child, kinsman, or relation; or holds back any portion from Him, is not upright in justice.