I am Muslim living in Ireland and I have a question which a lot of people keep asking me: Why slavery for men or women was not prohibited in Islam although Allah made all human with equal rights?

Islam came to find slavery existing in every part of the world. At that time, slavery was practiced through different means; people were enslaved through kidnapping and abduction, wars, and debts. Islam abolished all of these means with the exclusion of the enslavement of war prisoners. In its characteristic manner of introducing rulings, Islam did not abruptly abolish slavery but banned it by degrees to maintain social stability. The phenomenon of slavery existed in all the communities around the world and slaves were considered an important resource in the social and economic life of ancient times.

enslavement of prisoners of wars was legally institutionalized worldwide. Islam limited the sources of slavery with the aim of abolishing it; Islam prohibited enslaving anyone except those captured in battles when Muslims fought and defended themselves against tyrant enemies. This prohibition included the offspring of previously taken slaves. Islam allowed the enslavement of those who fought against Muslims in non-Muslim countries including women and children. However, it is only the Muslim ruler who was entitled to decide this according to what he sees as being in the best interest of Muslims. It was categorically forbidden to enslave anyone who did not fight Muslims. Enslaving a warrior is less evil than killing him. Islam prohibited the killing of female captives of war and substituted this with enslavement. In spite of this, Islam set certain ethics for the good treatment of slaves. It urged Muslims to treat them kindly and not harm them and prohibited any aggression against them.

Out of its eagerness for freeing all people, Islam expanded the means for emancipating slaves by making the manumission of a slave an of sins. These include breaking the fast in the month of Ramadan, zihar (wherein a husband deems his wife as unlawful to him as his mother), involuntary manslaughter, breaking oaths and the like. At the outset, Islam urged its followers to emancipate slaves and then limited the sources of slavery to help in its abolishment.

Islam commanded Muslims to treat slaves kindly until they obtained their freedom. This was stated in multiple texts of the shari'ah in which slaves were described as brothers to their masters since they shared with them the brotherhood of humanity which necessitated being merciful towards them and respecting their dignity. Mercy towards slaves was expanded and their emancipation was prescribed as an expiation for beating or abusing them.  As a result  of such great mercy towards slaves, people entered Islam in multitudes.

Islam observed a noble stance towards the institution of slavery; it limited its sources, increased the means towards their freedom, and exhorted Muslims to treat them kindly and emancipate them. This differed from what prevailed worldwide at that time and [the evil practices] of slave traders in later centuries after the discovery of the new world.

Slavery ended worldwide after the international treaty for the abolishment of slavery was signed in Berlin in 1860 AD. This has become a binding system that disallows anyone to enslave another.

Based on the above, slavery is impermissible in the Shari'ah. By virtue of the above mentioned treaty, all humans are deemed free and cannot be bought or sold. Muslims signed international treaties to end slavery which came in accordance with Islam's desire to limit its sources and expand the means towards freedom. Thus, all people are free as God the Almighty created them.