All praise belongs to Allāh who has legislated for us the paths of right guidance, warned us against all the paths that lead to doom and destruction, nipped all the evil ways of debauchery and indecency in the bud and commanded us to lower our gaze and guard our private parts. I bear witness that none is worthy of worship except Allāh, the Lord of the earth and the high heavens who creates and perfects and who designs and guides. I also bear witness that Muḥammad is His Servant and Messenger, the best of all mankind, who does not speak out of his own desire and who has been chosen by Allāh to convey His revelations. May Allāh bestow His peace and blessings upon him, upon his family and companions, symbols of piety and righteousness, as well as upon all those who follow in their footsteps.
Almighty Allāh sent His Messenger Muḥammad (ṣallallāhu `alayhi wa-sallam) as a mercy to all mankind, to enjoin upon them good, forbid them evil, make lawful for them the good things, forbid them the bad, guide them to sublime morals and best deeds and warn them against the evil ways of corrupt, misguided people. In fact, there is no good but he guided us to it and no evil but he warned us against it. The Islamic Law (Sharī'ah) came to guide us to all forms of good and warn us from all forms of evil in order for us to realise our common good in this life and attain eternal bliss in the hereafter. One of the evil sins against which the Sharī'ah texts have warned, and which all the divine laws have unanimously considered forbidden and warned those who commit it of a severe punishment, is the sin of adultery and fornication (zinā).
Given the seriousness and monstrosity of this sin and the multiplicity of its rulings and detrimental effects, it has been amply mentioned in the Qur'ānic verses and Prophetic traditions, and Muslim scholars have given special attention to it and discussed the various issues relating to it in many chapters in juristic books. One of the points relating to this issue and which has triggered a great deal of controversy among scholars is the ruling on marrying an adulteress, whether or not she has repented from such a sin or still persists in committing it, whether or not she can get married to the person with whom she committed adultery or to another man, for that matter, and whether or not she has given birth to illegitimate children. These and other points will be tackled in the present paper which I have titled "The Islamic Ruling of Marrying an Adulteress".
Rationale for Writing on this Issue
1. I lived in the Unites States of America for over five years, and while I was there I participated in a large number of conferences and set up numerous Islamic training courses in many parts of the United States, Canada, South America and many European countries. I also responded to questions posed by people seeking legal opinions on different issues verbally and in writing, in a number of newspapers and magazines in English and Arabic and also in the mass media and the Internet. One of the things that engaged my attention was the fact that a large number of people were requesting an advisory opinion on the issue of marrying an adulteress and the rulings regarding illegitimate children. This made me realise the importance of this issue and the dire need to research it and clarify rulings relating to it.
2. The huge controversy among scholars, past and present, about such issues and the cogent evidence brought forward by the different groups in support of their opinion has given rise to numerous ambiguities and an acute embarrassment to those involved in such matters, as this touches their marital lives and social relations and they become confused as to whether their marriage is valid or not and what is required of them in order to validate the marital relationship with those with whom they have had an affair, or with others, for that matter.
3. This problem is widespread among new Muslims who are bound to have one or more lovers whom they desire to marry but are not sure if such marriage would be valid or not, whether their lovers are required to repent before such marriage takes place and whether they are required to wait for the 'purification of the womb' process (known as istibrā') is over [by giving birth if she is pregnant or when her menses start] or not. In fact, many new Muslims had illegitimate relations with their wives before they married them, and they are uncertain as to whether such marriage is valid or not or whether or not they are required to renew the marriage contract. Furthermore, if they have had any illegitimate children, they do not know whether such children will derive their nasab (line of descent) from him or not, whether they will have custody of them instead of their mothers or whether to inherit from such children and vice versa.
4. This problem is prevalent in almost all societies including Muslim societies, albeit with a far lower percentage in the latter ones.
I will adopt a scientific and objective method in terms of gathering information from the primary sources, sorting it and arranging it in a logical order. I will also present the various pertinent issues in an objective manner by stating the points of agreement and disagreement, citing and discussing the evidence furnished by the different groups and stating the preponderant opinion which has more evidence in its favour and which is in total agreement with the ultimate objectives of the Sharī'ah. Extensive documentation of the various reports, quotations as well as footnotes is also included.
The paper consists of a foreword, an introduction, two chapters and a conclusion.
The introduction delineates the legitimacy and benefits of marriage as well as the prohibition of zinā  and its detrimental effects. The introduction consists of two sections: (1) Marriage and (2) Zinā. The first chapter discusses the issue of marrying a repentant adulteress and consists of two sections: (1) The ruling on marrying a repentant adulteress and (2) how the adulteress's repentance is established. The second chapter deals with the issue of marrying a non-repentant adulteress. The conclusion presents the main important findings of the study. I pray to Almighty Allāh to make the present study sincere for His Sake alone, in total agreement with the teachings of the Sharī'ah and highly beneficial to His servants; I also pray to Him to store its reward for me till I meet Him, for indeed He is Most Generous; and all praise is due to the Lord of the worlds.
The Legitimacy and Benefits of Marriage and the Prohibition of Zinā
Before embarking upon a thorough discussion of this issue, we shall first look at the linguistic and technical definitions of marriage (nikāh) and its legitimacy, then we shall look at the linguistic and technical definitions of zinā (adultery and fornication) and its prohibition.
a. Linguistic Definition of 'Marriage'
The Arabic word 'nikāḥ' (translated here as 'marriage') denotes 'coupling', 'putting together' and 'uniting'. When the action is attributed to trees, it denotes 'growing very close together', 'overlapping' and interlacing'. It also denotes sexual intercourse as well as the marriage contract. In fact, the Arabs have drawn a fine distinction between these two meanings. If the verb 'nakaḥa' (derived from 'nikāḥ') is used in connection with a man and a woman, it denotes marriage; if, however, it is used in connection with a man and his wife, then it denotes sexual intercourse. 
b. Technical Definition of 'Marriage'
Muslim scholars have expressed three opinions as to the technical definition of 'nikāḥ', as follows:
(1) it is used literally in connection with the marriage contract but used figuratively in connection with sexual intercourse;
(2) it is used literally in connection with sexual intercourse but used figuratively in connection with the marriage contract; and
(3) it used in its literal sense in connection with both the marriage contract and sexual intercourse.
The first opinion is the most correct one because the word 'nikāḥ' generally means 'marriage contract' unless there is evidence that states otherwise, for this is the very sense used in the Qur'ān, the Sunnah and explicitly expressed or understood in the terminology of Muslim jurists. 
Ibn Qudāmah writes, "There is no mention in [Allāh's] Book of the word 'nikāḥ' which means sexual intercourse with the exception of the verse "…and if he divorces her [for the third time] then she is not lawful for him thereafter until she marries (tankiḥa) another husband." This was the opinion of Ibn Qudāmah as well as a large number of Muslim scholars.  It has, however, been stated that the meaning of the word 'nikāḥ' in this verse is 'marriage contract'; for if the other husband has sexual intercourse with her without a marriage contract, she will by no means become lawful for her first husband, according to the unanimous agreement of all Muslim scholars.  The underlying meaning in the verse is that the marriage contract is sufficient in its own right, but the authentic Sunnah of the Prophet (ṣallallāhu `alayhi wa-sallam) clearly states that in addition to the marriage contract, marriage must also be fully consummated (i.e. sexual intercourse must take place; or, using the Prophet’s expression, "tasting each other’s sweetness' ('usayla, lit. Little honey)"). 
Ibn Ḥajar also writes, "...Setting the condition of sexual intercourse for [a wife] to be lawful to her husband again [after making three pronouncements of divorce on her], has been established in the Sunnah; the marriage contract is necessary, for the meaning of the word 'tankiḥa' [in the verse] means 'until she gets married, i.e. a marriage is contracted; it is clear that a marriage contract is sufficient, but the Sunnah has explained that after the conclusion of the marriage contract, sexual intercourse must also take place; after this divorce must also take place and then the waiting period following divorce ('iddah) is to be observed." 
Az-Zuhrī said in this regard, "The word 'nikāḥ' in the Book of Allāh is only known to mean marriage." 
Sheikh-al-Islām Ibn Taymiyyah also said, "Whenever the word 'nikāḥ' is mentioned in the Qur'ān, it only means the contract of marriage although this also includes sexual intercourse; however, it is never mentioned in the Book of Allāh to denote mere intercourse." 
As-San'ānī also said, "It (i.e. the word 'nikāḥ') has been extensively used to mean marriage contract; in fact, it has been said that it stands for a legal truth (haqīqah shar'iyyah)  and that it is only mentioned in the Glorious Book to denote marriage contract." 
In the terminology of Muslim jurists, nikāḥ means the marriage contract. Ibn Qudāmah said, "Were the word 'nikāḥ' to denote the marriage contract in a figurative sense, it would certainly have been a conventional word, which would solely denote the contract whenever it is uttered, for it would conventionally mean only that, as is the case with all conventional words." 
On the basis of the foregoing discussion, we can define 'nikāḥ' as "the valid contract of marriage even if sexual intercourse or khalwah  does not take place."
By saying 'contract', we exclude the possibility of zinā, for the latter constitutes sexual intercourse without a marriage contract; this intercourse may also take place without a contract, in which case the contract is not legally valid. This includes the case of a non-Muslim man contracting a marriage with a Muslim woman, a Muslim man contracting a marriage with a non-Muslim woman who is neither a Jewess nor Christian, contracting a marriage with any of one's near female relatives with whom it is unlawful to marry or contracting a marriage with the wife of another man or one who is mu'taddah ; for such a contract is null and void, and any intercourse that takes place in such cases is considered an act of zinā. Ibn Qudāmah said, "As to invalid marriages, such as marrying the wife of another man, a mu'taddah or similar women, if both parties are aware of the prohibition of such marriages, then they are considered adulterers and are subject to ḥadd , and the [illegitimate offspring] derives his or naṣab (line of descent) from neither of them."  By saying 'marriage', we exclude other kinds of contracts, such as sale contracts.
By saying 'valid', we exclude the kind of marriage that is null and void, such as nikāḥ ash-shubhah (mistaken marriage) , contracting a marriage without the consent of the guardian  of the woman, without publicizing the marriage or without two witnesses, for instance. We also exclude the invalid contract as mentioned above.
By saying 'even if sexual intercourse or khalwah does not take place', we mean that marriage can be established by merely concluding a marriage contract and thus such things as maintenance, inheritance and sexual intercourse apply even if no intercourse or khalwah takes place. If, for instance, one of the two spouses dies after the conclusion of the contract and before the consummation of the marriage, the other spouse is entitled to inherit from him or her. By the same token, if a man contracts a marriage with a woman but dies before the consummation of marriage, his wife cannot legally be married to his father, grandfather and on up and sons, grandsons and on down, according to the unanimous agreement of Muslim scholars.  Ash-Shawkānī said in this regard, "Muslim scholars are unanimously agreed that it is strictly forbidden for the sons to marry women with whom their fathers have contracted a marriage, and that it is also strictly forbidden for the fathers to marry women with whom their sons have contracted a marriage, for Allāh says,
'And do not marry those [women] whom your fathers married...' and '...and [also prohibited to you for marriage] are the wives of your sons who are from your [own] loins.'" 
Ash-Shanqītī also said, "Scholars are unanimously agreed that the woman with whom the father contracts a marriage becomes forbidden for marriage to the son even if the father has not had intercourse with her; similarly, the woman with whom the son contracts a marriage becomes legally forbidden for the father to marry even if the son has not had intercourse with her." 
 The Arabic word zinā includes both fornication and adultery. [Translator's Note]
 See Tahdhīb al-Lughah, 4/102; Lisān al-'Arab, 2/624; Al-Qāmūs al-Muhīt, p. 314; Talabat at-Talabah, p. 85; Sharh An-Nawawī, 9/171; Mughnī al-Muhtāj, 3/123; As-Sirāj al-Wahhāj, 1/359; Sharh Az-Zarqānī 'alā Muwatta' Mālik, 3/161; Al-Muqni' and Ash-Sharh al-Kabīr, 20/5-7; Matālib Ulī an-Nuhā, 5/3 and Subul as-Salām, 3/972.
 See Sharh An-Nawawī, 9/171; Al-Mughnī, 9/339; Fath al-Bārī, 9/103; Ash-Sharh al-Kabīr, 20/7; Sharh Az-Zarqānī 'alā Muwatta' Mālik, 3/161; Fath al-Wahhāb, 22/53 and Nayl al-Awtār, 7/258.
 Surat al-Baqarah, 2:230.
 See Tafsīr al-Qurtubī, 3/148.
 See Tafsīr at-Tabarī, 2/475.
 See Sharh Az-Zarqānī 'alā Muwatta' Mālik, 3/161.
 Fath al-Bārī, 9/103.
 Tahdhīb al-Lughh, 4/103 and Lisān al-'Arab, 2/625.
 Majmū' al-Fatāwā Ibn Taymiyyah, 32/113.
 This means the word is used for the meaning for which it has legally been coined, and the One who originally used it for this purpose is the Lawgiver (Almighty Allāh). The Arabic word 'salāh' is a case in point; for it denotes an act of worship which consists of certain well-known statements and actions. [Translator's Note]
 Subul as-Salām, 3/972.
 Al-Mughnī, 9/340.
 The meaning of being alone (khalwah, literally seclusion) is when a man and a woman who are not immediate family members (maḥram) remain alone in a room or place in a way that a third person is not easily able to enter upon them, or it is not usually accessible to others. This also (according to the scholars) includes a room/area, the door of which is closed, even if it may not be locked. [Translator's Note]
 A mu'taddah is a woman in her 'iddah, or period of probation after the death of her husband or after her divorce. [Translator's Note]
 Ḥadd (plural: ḥudūd) refers to the specific punishment assigned by the Qur'ān and the Sunnah for particular crimes. [Translator's Note]
 Al-Mughnī, 9/354.
 This occurs when, for instance, copulation mistakenly takes place because the man and woman mistakenly believe themselves to be husband and wife. [Translator's Note]
 In the Islamic law of marriage, the wali (translated here as guardian) is a woman's closest adult male relative, who has authority and responsibility with respect to her marrying; in this context, wali can be translated "marriage guardian." [Translator's Note]
 See footnote 14. [Translator's Note]
 Al-Baḥr ar-Rā'iq, 3/82.
 Surah an-Nisā', 4:22.
 Surah an-Nisā', 4:23.
 Fath al-Qadīr, 1/446.
 Aḍwā' al-Bayān, 1/315; see also Al-Mughnī, 9/524, Ash-Sharh al-Kabīr, 7/475 and Manār as-Sabīl, 2/163.