نكاح الكفار
Ibn ‘Abbās (may Allah be pleased with him) reported: A woman converted to Islam during the lifetime of the Messenger of Allah (may Allah's peace and blessings be upon him) and got married. So, her husband came to the Prophet (may Allah's peace and blessings be upon him) and said: "O Messenger of Allah, I had embraced Islam and she knew of my conversion." Therefore, the Messenger of Allah (may Allah's peace and blessings be upon him) separated her from her new husband and restored her to her first husband.
عن ابن عباس قال: أسْلَمت امرأة على عهد رسول الله -صلى الله عليه وسلم- فتزوجت، فجاء زوجها إلى النبي -صلى الله عليه وسلم-، فقال: يا رسول الله إني قد كنت أسلمت، وعَلِمَتْ بإسلامي، «فانتزعها رسول الله صلى الله عليه وسلم من زوجها الآخر، وردَّها إلى زوجها الأول».
شرح الحديث :
This Hadīth indicates that a woman became Muslim during the Prophet's lifetime and then got married. Her husband told the Prophet (may Allah's peace and blessings be upon him) that he had become Muslim. Therefore, the Prophet (may Allah's peace and blessings be upon him) annulled the second marriage and restored the woman to her first husband because she was still his legal wife as long as he was Muslim. This Hadīth indicates that if a husband becomes Muslim and his wife knows of his conversion, she is still his legal wife. If she marries someone else, this new marriage is invalid, and thus she is to be separated from the new husband.