Firstly, slavery doesn't exist in modern world (including the Muslim world). However, in pre-Islamic era, there was too much injustice towards the slaves and people used to take slaves for every silly reason. Islam restricted it to war prisoners only. When Islam came it started treating them justly and slowly emancipating them. In fact, we have a book of Emancipation of Slaves which has Prophetic tradition and commands to treat slaves justly and emancipate them.
Secondly, Islam allows a man to have intercourse with his slave woman. A slave woman with whom a man has intercourse is known as a sariyyah (concubine) from the word sirr, which means marriage.
Allaah says (interpretation of the meaning):
“O Prophet (Muhammad)! Verily, We have made lawful to you your wives,
to whom you have paid their Mahr (bridal‑money given by the husband to
his wife at the time of marriage), and those (slaves) whom your
right hand possesses — whom Allaah has given to you, and the
daughters of your ‘Amm (paternal uncles) and the daughters of your
‘Ammaat (paternal aunts) and the daughters of your Khaal (maternal
uncles) and the daughters of your Khaalaat (maternal aunts) who
migrated (from Makkah) with you, and a believing woman if she offers
herself to the Prophet, and the Prophet wishes to marry her a
privilege for you only, not for the (rest of) the believers. Indeed We
know what We have enjoined upon them about their wives and those
(slaves) whom their right hands possess, in order that there should be
no difficulty on you. And Allaah is Ever Oft‑Forgiving, Most Merciful”
“And those who guard their chastity (i.e. private parts from illegal
Except from their wives or the (women slaves) whom their right hands
possess for (then) they are not blameworthy.
But whosoever seeks beyond that, then it is those who are trespassers” [al-Ma’aarij 70:29-31]
Ibraaheem (peace be upon him) took Haajar as a concubine and she bore him Ismaa’eel (may peace be upon them all).
BUT, there are those who argue that since Islam permits Muslim men to have sexual intercourse with their slave girls, this then means that they also have the right to rape them.
This is absurd. The right to have sex with a woman does not necessarily imply that one has the right to rape her as well. To say that a Muslim man has the right to rape his slave girl is like saying that a man has the right to rape his wife, which is not true.
Rape in Islam is completely forbidden.
Imam Maalik said:
In our view the man who rapes a woman, regardless of whether she is a
virgin or not, if she is a free woman he must pay a "dowry" like that
of her peers, and if she is a slave he must pay whatever has been
detracted from her value. The punishment is to be carried out on the
rapist and there is no punishment for the woman who has been raped,
whatever the case. (Imam Maalik, Al-Muwatta', Volume 2, page 734)
Imam Al Shaafi'i said:
"If a man acquires by force a slave-girl, then has sexual intercourse
with her after he acquires her by force, and if he is not excused by
ignorance, then the slave-girl will be taken from him, he is required
to pay the fine, and he will receive the punishment for illegal sexual
intercourse." (Imam Al Shaafi'i, Kitaabul Umm, Volume 3, page 253)
These two people are some of the famous classical scholars of Islam.
In an authentic narration from Sunan Al Bayhaqi, Volume 2, page 363, Hadith no. 18685, the following story comes:
Abu al-Hussain bin al-Fadhl al-Qatan narrated from Abdullah bin Jaffar
bin Darestweh from Yaqub bin Sufyan from al-Hassab bin Rabee from
Abdullah bin al-Mubarak from Kahmas from Harun bin Al-Asam who said:
Umar bin al-Khatab may Allah be pleased with him sent Khalid bin
al-Walid in an army, hence Khalid sent Dharar bin al-Auwzwar in a
squadron and they invaded a district belonging to the tribe of Bani
Asad. They then captured a pretty bride, Dharar liked her hence he
asked his companions to grant her to him and they did so. He then had
sexual intercourse with her, when he completed his mission he felt
guilty, and went to Khalid and told him about what he did. Khalid
said: 'I permit you and made it lawful to you.' He said: 'No not until
you write a message to Umar'. (Then they sent a message to Umar) and
Umar answered that he (Dharar) should be stoned. By the time Umar's
message was delivered, Dharar was dead. (Khalid) said: 'Allah didn't
want to disgrace Dharar'
Notice that Umar ibn Al Khattab (the second caliph) ordered the man who captured the slave girl and had sex with her to be stoned for this crime, for he took the slave girl unjustly.
And Umar ibn Al Khattab is one of the Caliphs of Islam and one of the most loved companions of the Prophet salallahu alayhi wassalm.
It is nonsense to suggest that one could rape the slave girl he possesses because the Prophet (peace be upon him) warned us that we must take good care of those under our authority:
"There is no person to whom Allaah has given people to take care of,
and he fails to take care of them properly, but he will not smell the
fragrance of Paradise." (Saheeh Bukhari no. 6731; Saheeh Muslim, no.
Umar ibn al-Ahwas (may Allaah be pleased with him) reported that he heard the Messenger of Allaah SAWS (peace and blessings of Allaah be upon him) say during his Farewell Pilgrimage:
"Verily, you have rights over your women, and your women have rights
over you. As for your rights over your women, they are that they
should not allow anyone to sit on your beds whom you dislike, or allow
anyone into your houses whom you dislike. Verily, their rights over
you are that you should treat them well with regard to their clothing
and food." (Reported by al-Tirmidhi, 1163, and Ibn Maajah, 1851).
The Prophet (peace be upon him) made it clear that we shouldn't harm slaves:
Saheeh Bukhari: Volume 1, Book 2, Number 29
Narrated Al-Ma'rur: At Ar-Rabadha I met Abu Dhar who was wearing a
cloak, and his slave, too, was wearing a similar one. I asked about
the reason for it. He replied, "I abused a person by calling his
mother with bad names." The Prophet said to me, 'O Abu Dhar! Did you
abuse him by calling his mother with bad names You still have some
characteristics of ignorance. Your slaves are your brothers and Allah
has put them under your command. So whoever has a brother under his
command should feed him of what he eats and dress him of what he
wears. Do not ask them (slaves) to do things beyond their capacity
(power) and if you do so, then help them.
The Prophet (peace be upon him) said that our slaves are like our siblings. Who would rape his own sister?
The Prophet (peace be upon him) forbade causing physical harm to slaves:
Saheeh Muslim Book 015, Number 4082:
Hilal b. Yasaf reported that a person got angry and slapped his
slave-girl. Thereupon Suwaid b. Muqarrin said to him: You could find
no other part (to slap) but the prominent part of her face. See I was
one of the seven sons of Muqarrin, and we had but only one slave-girl.
The youngest of us slapped her, and Allah's Messenger (may peace be
upon him) commanded us to set her free.
Book 015, Number 4086
Abu Mas'ud al-Badri reported: "I was beating my slave with a whip when
I heard a voice behind me: Understand, Abu Masud; but I did not
recognise the voice due to intense anger. He (Abu Mas'ud) reported: As
he came near me (I found) that he was the Messenger of Allah (may
peace be upon him) and he was saying: Bear in mind, Abu Mas'ud; bear
in mind. Abu Mas'ud. He (Aba Maslad) said: threw the whip from my
hand. Thereupon he (the Holy Prophet) said: Bear in mind, Abu Mas'ud;
verily Allah has more dominance upon you than you have upon your
slave. I (then) said: I would never beat my servant in future.
If the Prophet (peace be upon him) forbade slapping and whipping slaves then it's unthinkable that he would have permitted raping them. It just makes no sense.
Thus, our argument is as follows:
The Prophet (peace be upon him) has prohibited causing harm to and oppressing those under our authority.
Rape is causing harm to someone and is considered a form of oppression.
If the critic says that the Prophet (peace be upon him) made an exception to this general prohibition by allowing one to rape his slave girl, the burden of proof is upon him to show evidence for this exception.
If he is not able to show evidence for this exception then we must assume that the Prophet's (peace be upon him) general command is upheld, thus proving that Islam forbids one to rape his slave girl.
I added some parts from a long and wide article on "Does Islam Permit Muslim Men to Rape Their Slave Girls? By Bassam Zawadi"
There are more examples where the Prophet Salallahu alayhi wassalam clearly forbid his people from doing any physical injustice to their slaves. That will just make this post longer. I hope there is no requirement for that.