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Surah 4. An-Nisaa'
Ayah 25
25وَمَن لَّمْ يَسْتَطِعْ مِنكُمْ طَوْلًا أَن يَنكِحَ ٱلْمُحْصَنَـٰتِ ٱلْمُؤْمِنَـٰتِ فَمِن مَّا مَلَكَتْ أَيْمَـٰنُكُم مِّن فَتَيَـٰتِكُمُ ٱلْمُؤْمِنَـٰتِ ۚ وَٱللَّهُ أَعْلَمُ بِإِيمَـٰنِكُم ۚ بَعْضُكُم مِّنۢ بَعْضٍ ۚ فَٱنكِحُوهُنَّ بِإِذْنِ أَهْلِهِنَّ وَءَاتُوهُنَّ أُجُورَهُنَّ بِٱلْمَعْرُوفِ مُحْصَنَـٰتٍ غَيْرَ مُسَـٰفِحَـٰتٍ وَلَا مُتَّخِذَٰتِ أَخْدَانٍ ۚ فَإِذَآ أُحْصِنَّ فَإِنْ أَتَيْنَ بِفَـٰحِشَةٍ فَعَلَيْهِنَّ نِصْفُ مَا عَلَى ٱلْمُحْصَنَـٰتِ مِنَ ٱلْعَذَابِ ۚ ذَٰلِكَ لِمَنْ خَشِىَ ٱلْعَنَتَ مِنكُمْ ۚ وَأَن تَصْبِرُوا۟ خَيْرٌ لَّكُمْ ۗ وَٱللَّهُ غَفُورٌ رَّحِيمٌ
[25] Whoever cannot afford to marry free Muslim women, should marry one of the Muslim slave-girls in your possession; Allah has full knowledge of your Faith. You all belong to one and the same community;45 therefore, you may marry them with the permission of their guardians and give them their fair dowries so that they may live a decent life in wedlock and not in licentiousness nor may have secret illicit relations. Then if they are guilty of indecency, after they have been fortified by wedlock, they shall be given half the punishment prescribed for free women.46 This concession47 has been made for those of you who might apprehend a moral lapse without marriage, but it is better for you to practice self-restraint, and Allah is Forgiving, Merciful.
45That is, "The social differences among the people are merely relative; otherwise all Muslims are equal. As a matter of fact, the thing that distinguishes one Muslim from another is the quality of his Faith, and that is not the monopoly of the higher ranks of society. It is just possible that a Muslim slave-girl is higher in rank in regard to belief and morality than a free woman of a high family.
46It should be kept in view that in this section (vv. 2425) the Arabic word muhsanat has been used in two different senses: (1) "wedded wives", enjoying the protection of their husbands; and (2) "free Muslim women" enjoying the protection of their families, even though they might not be married. This is important, because the lack of differentiation between these two meanings has given rise to a superficial complication. The Kharijites and those others who do not believe in the stoning of an adulterous woman have misconstrued this verse (25) to prove their own point of view. They argue that in this verse, the punishment prescribed for an adulterous married slave-girl is half of the punishment prescribed for a free "married" Muslim woman. If the punishment for an adulterous free married woman had been stoning to death, there could be no half of this punishment for a guilty slave-girl. Hence, this verse is, according to them, a conclusive proof that the punishment of stoning does not exist in Islam.
The fallacy of the above argument becomes obvious, if one uses common sense in the application of the appropriate meaning of muhsanat. In the case of the guilty slave-girl, it has been used in the sense of "married woman", enjoying the protection of the husband, as is plain from the subsequent clause; "after they have been fortified in wedlock". But in the case of the guilty Muslim woman, half of whose punishment is to be given, it means "free Muslim woman" enjoying the protection of her family, and does not mean a "free married Muslim woman", as has been misconstrued by the opponents of the punishment of stoning.
As regards the lighter punishment for an adulterous slave-girl than for a free Muslim woman, it is based on the fact that the latter enjoys double protection as compared with the former the protection of the family (even though she be unmarried) and the protection of the husband, which reinforces the protection of the family she already enjoys. In contrast to a free woman, a slave-girl does not enjoy any protection at all, if she is unmarried, and even after marriage her position does not become equal to that of an un-married free Muslim woman, for the latter enjoys the protection of her status, her family, her clan, etc. On the other hand, a slave-girl still remains, to some extent, under the bondage of slavery and has no protection of the family, clan, etc. Therefore, her punishment should be half of an un-married free woman and not half of a free married woman.
Furthermore this also shows that the punishment of one hundred stripes as prescribed in An-Nur, XXIV : 2, is for an un-married free Muslim woman guilty of fornication half of which has been prescribed here for a slave married girl. As for an adulterous married free woman she deserves capital punishment for this heinous crime because she enjoys the double protection of the family and of the husband, and that punishment is "stoning her to death." Though the Qur'an does not explicitly mention the punishment of stoning to death, it does indicate it in a subtle manner, which the Holy Prophet understood and enforced. And who else could understand the Qur'an better?
47The "concession" is to marry one of the slave-girls with the consent of her master if one cannot afford to marry a free Muslim woman.