This is taken from the book; Islamic Jihad; A legacy of forced conversion, imperialism and slavery, by M.A Khan.
THE QURANIC SANCTION OF SLAVERY
The institution of slavery in Islam was formalized in the following Quranic verse, in which Allah distinguishes free human beings or masters, who exercise justice and righteousness, from the dumb, useless and burdensome ones, the slaves:
Allah sets forth (another) Parable of two men: one of them dumb, with no power of any sort; a wearisome burden is he to his master; whichever way he directs him, he brings no good: is such a man equal with one who commands Justice, and is on a Straight Way? [Quran 16:76]
Allah warns the believers against taking the slaves as equal partner in status and in sharing their wealth, lest they have to fear them as anyone else:
…do ye have partners among those whom your right hands possess (i.e., slaves, captives) to share as equals in the wealth We have bestowed on you? Do ye fear them as ye fear each other? [Quran 30:28]
Allah recognizes some human beings, namely the masters, as more blessed by Himself than the less favored slaves as part of His divine plan. He warns Muslims against sharing His gifts to them equally with their slaves. Those who would take slaves as equal, warns Allah, would deny Him:
Allah has bestowed His gifts of sustenance more freely on some of you than on others: those more favoured are not going to throw back their gifts to those whom their right hands possess, so as to be equal in that respect. Will they then deny the favours of Allah? [Quran 16:71]
Allah does not only sanction the institution of slavery, He also gave divine blessing to masters (Muslim men only can own slaves) to have sex with the female slaves:
And those who guard their private parts, Except in the case of their wives or those whom their right hands possess—for these surely are not to be blamed [Quran 70:29–30]
And who guard their private parts, except before their mates or those whom their right hands possess, for they surely are not blameable [Quran 23:5–6]
Therefore, if there are women amongst the captives or slaves, Muslims are divinely sanctioned to have sex with them as they do with their wives. This verdict of Allah founded the institution of sex-slavery or slave-concubinage in Islam, which was widespread in the pre-colonial Muslim world and continued well into the mid-twentieth century. As far as legal marriage is concerned, there is a limitation of four wives for a man at one time [Quran 4:3], but no such limitation on the number of sex-slaves.
Allah also gave a divine sanction to Muslims for acquiring female slaves for sexual engagement by waging wars against the infidels:
O Prophet! surely We have made lawful to you your wives whom you have given their dowries, and those whom your right hand possesses out of those whom Allah has given to you as prisoners of war… [Quran 33:50]
Muslims can engage in sex with the captured slave women even if they are married, but not with the married free Muslim women:
Also (prohibited are) women already married, except those whom your right hands possess… [Quran 4:24].
There are other verses in the Quran that talks approvingly of slaves and capturing them in wars. Thus, according to the divine commands of the Islamic God as enshrined in the holy Quran, Muslims are allowed to keep slaves. They can amass slaves by waging wars, have sex with the female slaves, and of course, use them as they wish. For Muslims, having sex with female slaves is as legal as having sex with their married wives. Slavery appears to be one of the most desired divine privileges in Islam, since Allah took the pain of reminding Muslims about this divine right time and again in so many verses.
THE PROPHETIC MODEL OF SLAVERY
Allah did not rest with repeatedly reminding Muslims to engage in slavery, but also took the initiative to guide Prophet Muhammad on how to enslave the infidels, such as in the following verse:
And He (Allah) brought those of the People of the Scripture (i.e., Banu Qurayza) who supported them (i.e., the Quraysh) down from their strongholds, and cast panic into their hearts. Some (adult males) ye slew, and ye made captive some (women and children)… [Quran 33:26–27]
In this verse, Allah charged the Banu Qurayza Jews with supporting the Quraysh of Mecca “from their strongholds” against Muslims in the battle of the Trench (627). Based on this unsubstantiated accusation, Allah commanded that some of the Jews, the adult males, were to be slain, and the rest, the women and children, enslaved. The Prophet duly complied with this divine command. He distributed the enslaved women and children among his disciples, himself acquiring one-fifth of them. The young and pretty ones amongst the female captives were made sex-slaves; the Prophet himself took beautiful Rayhana, whose husband and family members had been slain in the massacre. He took her to bed on the same night.
After conquering Khaybar the following year, Muhammad carried away their women and children as slaves. In many other attacks, the Prophet and his followers enslaved and carried away the women and children of the vanquished. Therefore, after aggressively attacking and defeating the infidels, enslaving the women and children became a model of Muhammad’s wars. Some of the slaves could be sold or ransomed for generating revenues. The young and pretty ones amongst the female captives became sex-slaves.
Since emulating Muhammad in action and deed is central to living a good Muslim life in Islamic thought, Muslims duly embraced his model of slavery (comprising enslavement, slave-trade and slave-concubinage) and perpetuated it during the later centuries of Islamic domination. Muhammad’s example of dealing with the Jews of Banu Qurayza or Khaybar became the standard template for capturing slaves. This led to a massive rise in enslavement, sex-slavery and slave-trade in medieval Islamdom. After Muhammad’s death, Muslims—armed with sanctions of the Quran and Sunnah—embarked on an unbridled mission of waging holy war to conquer the world for the purpose of spreading Islam and expanding Islamic rule. As Islam burst out of Arabia, Muslim invaders became adept at capturing the vanquished infidels, particularly the women and children, in large numbers as slaves.
In Islamic thoughts (as noted already), the civilizations preceding and outside of Islam are jahiliyah or erroneous in nature, invalidated with the coming of Islam. Only Muslims were in the sole possession of truth in the form of the true faith of Islam. In their thoughts, the world outside the boundary and religion of Islam, notes Bernard Lewis, ‘was inhabited by the infidels and barbarians. Some of these were recognized as possessing some form of religion and a tincture of civilization. The remainder, polytheists and idolaters, were seen primarily as sources of slaves.’ Muslims captured slaves in such great numbers that slave-trade became a booming business enterprise; markets across the Muslim world became teeming with slaves. Accordingly, ‘it goes to the credit of Islam to create slave trade on a large scale, and run it for profit like any other business,’ writes Lal.