“O ye who believe! Stand out firmly for justice, as witnesses to God, even against yourself, or your parents, or your kin, and whether it be (against) rich or poor.” (4:135) 

But Islamic justice is something higher than the formal justice of Roman law or any other human law. It is even more penetrative than the subtler justice in the speculation of the Greek philosophers. It reaches out innermost motives, because we are to act as in the presence of God, to whom all things, act and motives are known. 

Justice, even at the detriment of self-interest (Qur'an 4:135 above), such is what Islam enjoins on Muslims in all their conduct, including that in Foreign and War Offices. In his book, Abu ‘Abaid quotes this saying of the Prophet p.b.u.h “Observance for violation is better than violation for violation” – M. Hamidullah, Muslim Conduct of State (page 76). 

• One cannot transgress law and justice and good conscience on the pretext that the other party is non-Muslim. 
• One cannot violate pledge given them on any account. 
• Vicarious reprisals are unlawful in Islam (for practice see “hostages” under the chapter ‘End of War’, ibid para 577) Or again, the Islamic institution of giving quarter to the enemy, based on the Quranic command concerns none else than the polytheists, the most detested of all the non-Muslims in Islam, if any human being asks for asylum and protection, it can on no account be refused. 

The Quran clearly declares in 4:136: 

“O ye who believe! Believe in God and His Apostle, and the Scripture, which He hath sent to His Apostle, and the Scripture, which He has sent to those before (him). Any who denieth God, His angels, His Books, His Apostles, and the Day of Judgement, hath gone far, far astray.”  [see commentary 646]

Treatment of aliens has always been a matter of fundamental and far-reaching importance throughout history. Enemies from among the brothers have always elicited some restraint on the part of the victors, but the aliens have never been so fortunate. It is a matter of historical record that genocide was a religious dogma for some (regarding the Amalekites), untouchability for others,  [whereas others said] “to violate a pledge is a sin, yet to honour the pledge given to the infidel is a greater sin” (as we heard during the Crusades). 

It is important to note in conclusion that Muslim jurists have always treated the subject of treatment of aliens/non-Muslims i.e. the international law as an integral part of the general Muslim law. They do not leave this to the discretion of the rulers or the whims and fancies of politicians. The earliest extant manual or code of Muslim law dating back to the very first century was compiled by Zaid ibn Ali (grandson of Khalifa Ali) (d.120H.) under the title of Almajmu’.