There is no question that Islam affirms the marriages that took place outside of Islam or before a person embraced Islam. The evidence for this is numerous. For example, in Soorah al-Masad, Allah refers to the wife of Abu Lahab, the Prophet’s uncle who vigorously opposed him, as well as to the wife of the Pharaoh. Numerous Companions of the Prophet (peace and blessings of Allah be upon him) were born before the advent of Islam and they were considered legitimate children of their parents. Indeed, the Prophet (peace and blessings of Allah be upon him) never ordered married Companions to remarry within Islam. In fact, the Prophet (peace and blessings of Allah be upon him) did not even ask them about the circumstances of their marriage contract, such as whether there were witnesses and so forth.
However, those relationships that were considered illegitimate by a convert's previous religion or law are also considered illegitimate in Islam. Thus, for example, one’s illegitimate child before embracing Islam remains illegitimate after one's embracing of Islam.101 On the other hand, any children born via a legitimate pre-Islamic marriage will be considered legitimate children and continue to be the children of the Muslim convert.
One exception to this general principle of affirming pre-Islamic marriages is where the husband and wife are within the prohibited degrees of marriage. Thus, for example, in ancient Persia, brothers and sisters could marry one another. Such a marriage would be considered void as soon as either of the couple embraced Islam. Furthermore, in a polygynous situation, if a man is married to more than four wives, upon embracing Islam he must separate from some of them and may have, at the most, only four wives.
Some other important issues related to conversion to Islam must be touched upon. If a husband and a wife both embrace Islam at approximately the same time, then their marriage remains in tact and there is no need for them to take any further steps. If a man who is married to either a Christian or Jewish woman embraces Islam, the marriage also remains in tact and there is also no need for any further steps.102 Those cases are clear and non problematic.
The problematic cases are:
(1) a male convert married to a woman who is not Christian, Jewish or accepting of Islam;
(2) a female convert married to a non-Muslim husband.103
The pertinent verses of the Quran related to these issues are as follows: Allah says, “O you who believe! When believing women come to you as emigrants, examine them, Allah knows best as to their faith. Then if you ascertain that they are true believers, send them not back to the disbelievers, they are not lawful (wives) for the disbelievers nor are the disbelievers lawful (husbands) for them” (60:10).
Allah also says, “And do not marry polytheistic women till they believe (and worship Allah Alone). And indeed a slave woman who believes is better than a (free) polytheistic woman, even though she pleases you. And give not (your daughters) in marriage to polytheistic men till they believe (in Allah Alone) and verily, a believing slave is better than a (free) polytheistic man, even though he pleases you. Those [polytheists] invite you to the Fire, but Allah invites (you) to Paradise and Forgiveness by His Leave, and makes His signs clear to mankind that they may remember” (2:221).
According to ibn al-Qayyim, when a woman married to a non-Muslim converts to Islam, the marriage becomes suspended and non-binding. In other words, she no longer is his wife in the sense of having marital relations or him being financially responsible for her.104 However, the woman is free to choose between ending the marriage (thereby being free to marry somebody else but only after her waiting period is finished) or suspending the marriage in the sense of waiting for her husband to embrace Islam. In the latter case, whenever the man embraces Islam, the woman automatically returns to him as a wife with no need for a new marriage contract, even if the husband's conversion took place many years after that of the wife.
The strongest evidence for this conclusion is the case of the Prophet’s own daughter, Zainab. She embraced Islam but her husband, Abu al-Aas ibn al- Rabee, refused to do so for many years. Then, finally, after six years, he came to Madinah and the Prophet (peace and blessings of Allah be upon him) reunited the couple without a new marriage contract or dower.105
If a man embraces Islam and his wife is not a Muslim, Jew or Christian, then his retaining her as a wife will be harmful to her, as he will not be allowed to have marital relations with her or treat her as a full wife. Thus, in this case, the marriage comes to an end if the woman refuses to embrace Islam. Allah says, “Likewise hold not the disbelieving women as wives” (60:10).
101 Cf., Muhammad ibn Abu Bakr ibn Qayyim al-Jauziyyah. Ahkaam Ahl al-Dhimmah (Damam, Saudi Arabia: Zamaadi li-l-Nashr, 1997), vol. 2, pp. 764f.
102 This is based on the verse, “Made lawful to you this day are all good things. The food of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time, when you have given their due bridal money, desiring chastity not committing illegal sexual intercourse, nor taking them as girl-friends” (5:5).
103 Although there is a great deal of difference of opinion concerning some of these issues, the author is following the conclusions reached by ibn al-Qayyim in Ahkaam Ahl al-Dhimmah (vol. 2, pp. 640-695). Ibn al-Qayyim has discussed these questions in great detail and has supported his opinion with strong, conclusive arguments.
104 He is not financially responsible for her because she is the one choosing this option while at the same time she is not making herself available to him as a wife.
105 Ibn al-Qayyim (vol. 2, p. 650) also presents a story in which Zainab’s husband was coming to Madinah and she asked the Prophet (peace and blessings of Allah be upon him) whether he could stay at her residence. The Prophet (peace and blessings of Allah be upon him) told her, “He is your husband but he cannot be in [physical] contact with you.” This demonstrates that the marriage is suspended. It is neither a full marriage nor are the two completely separated. Unfortunately, though, this author was not able to trace this story through any other sources besides this reference.