Allaah سبحانه و تعالى says, "Verily! Allah commands that you should render back the trusts to those, to whom they are due; and that when you judge between people, you judge with justice. Verily, how excellent is the teaching which He (Allah) gives you! Truly, Allah is Ever All-Hearer, All-Seer."
Mufti Muhammad Shafi' رحمه الله comments,
"It should be noted that Allaah Almighty has said, 'between people', and not 'between Muslims,' or 'between believers.' Thus, the hint given is that all human beings are equal in the sight of the decider of cases in disputes. They may be Muslims or non-Muslims, friends or enemies, or they may belong to the same country, colour, language, or they may be from another country, differ in colour and speak a different language. Those who have been made responsible to judge between them are duty-bound to cast aside all these connections and give their decision guided by whatever be the dictate of truth, right and just. ...It is the standing duty of those in authority that they should, whenever a case comes to them, give a judgement based on equity and justice without making any discrimination on the basis of race, country of origin, colour, language, even religion and creed." [Ma'ariful Qur'an, vol. 2, pp. 473-474]
See also: There is no racism in Islam!