The Prophet (may Allah's peace and blessings be upon him) returned his daughter Zaynab to …

Zaynab (may Allah be pleased with her) was the oldest daughter of the Prophet (may Allah's peace and blessings be upon him). She was married to Abu al-‘Ās ibn Ar-Rabī‘. She had converted to Islam and emigrated before her husband embraced Islam and emigrated. When her husband entered Islam and emigrated, the Messenger of Allah (may Allah's peace and blessings be upon him) returned Zaynab to him after six years (according to this narration), without concluding a new marriage contract for her. Some scholars deduced from this Hadīth that if a disbelieving husband does not become a Muslim during his wife's waiting period, which then expires, then the marriage is not dissolved. Still, the woman has the choice of going back to him or marrying another man. The majority of Muslim jurists, however, believe that this form of marriage is dissolved. They used other Hadīths to support their opinion. They remarked that when Zaynab embraced Islam and her husband remained a disbeliever, the Prophet (may Allah's peace and blessings be upon him) did not separate between them, for it was not yet revealed that a Muslim woman is forbidden to marry a disbeliever. When this was revealed {They are not lawful [wives] for them, nor are they lawful [husbands] for them} [Sūrat al-Mumtahanah: 10], the Prophet (may Allah's peace and blessings be upon him) commanded Zaynab to observe her waiting period. Abu al-‘Ās arrived as a Muslim before the waiting period expired, and thus the Prophet (may Allah's peace and blessings be upon him) kept the spouses in their marriage. By this understanding, the Hadīth is no longer confusing. The fatwa of the Permanent Committee follows the majority of scholars stating: If a non-Muslim couple enter Islam together, they keep their marriage. The disbelievers used to convert to Islam along with their spouses, during the lifetime of the Prophet (may Allah's peace and blessings be upon him) and he would keep them married. But, if one spouse only becomes a Muslim, the couple should be separated. If the other spouse converts during the waiting period, the couple would keep their marriage. If the other spouse does not convert during the waiting period, the marriage dissolves. In this respect, Allah, the Almighty, says: {And if you know them to be believers, then do not return them to the disbelievers; they are not lawful [wives] for them, nor are they lawful [husbands] for them. But give the disbelievers what they have spent. And there is no blame upon you if you marry them when you have given them their due compensation. And hold not to marriage bonds with disbelieving women.} [Sūrat al-Mumtahanah: 10]