What is the ruling on a Muslim man marrying a disbelieving woman who embraced Islam while her disbelieving husband has not divorced her? And does her waiting period (iddah) begin from the day of her divorce or from the day of her embracing Islam?

If the wife embraces Islam while her husband remains a disbeliever, she becomes unlawful to him. The separation depends on the expiration of her waiting period (iddah) from the time of her conversion to Islam. If the husband embraces Islam before her iddah expires, the marriage remains valid. If he does not embrace Islam until her iddah expires, she becomes free to make her own decision and it becomes lawful for her to marry someone else. This is what Ibn Qudamah and the scholars of the Permanent Committee for Issuing Fatwas have affirmed, citing the Almighty’s saying: "Then if you ascertain that they are believers, do not return them to the disbelievers; neither are they lawful for them, nor are they lawful for them." And it is permissible for the woman to marry after the expiration of her iddah without needing a divorce from her disbelieving husband. However, in non-Islamic countries, she might need to officially prove her separation to prevent potential harms.