Surah Al Mumtahanah Tafseer

وَإِن فَاتَكُمْ شَيْءٌ مِّنْ أَزْوَاجِكُمْ إِلَى الْكُفَّارِ فَعَاقَبْتُمْ

فَأتُوا الَّذِينَ ذَهَبَتْ أَزْوَاجُهُم مِّثْلَ مَا أَنفَقُوا

And if any of your wives have gone from you to the disbelievers -- then you succeeded (gained victory) over them; then pay those whose wives have gone, the equivalent of what they had spent.

Mujahid and Qatadah explained this Ayah, by saying,

"This is about the disbelievers who did not have a treaty of peace. If a woman flees to the disbelievers and they do not give back what that her husband spent on her, then if a women comes to them (the Muslims) they are not to return to her husband anything until they pay the Muslim whose wife went to them the equivalent of what he spent."

Ibn Jarir recorded that Az-Zuhri said,

"The believers abided by Allah's decree and paid what they owed the idolators to compensate for the dowry the idolators gave to the women (who emigrated). However, the idolators refused to accept Allah's judgement for what they owed the Muslims. Allah said to the faithful believers,

وَإِن فَاتَكُمْ شَيْءٌ مِّنْ أَزْوَاجِكُمْ إِلَى الْكُفَّارِ فَعَاقَبْتُمْ

فَأتُوا الَّذِينَ ذَهَبَتْ أَزْوَاجُهُم مِّثْلَ مَا أَنفَقُوا

وَاتَّقُوا اللَّهَ الَّذِي أَنتُم بِهِ مُوْمِنُونَ

And if any of your wives have gone from you to the disbelievers -- then you succeeded (gained victory) over them; then pay those whose wives have gone, the equivalent of what they had spent. And have Taqwa of Allah, the One in Whom your are believers.

Therefore, if a Muslim woman reverts to the idolators, the believers should give back the dowry her Muslim husband paid her, from whatever money is left with them from the dowry of women who migrated to the Muslims. They were supposed to return this wealth to the idolator husbands of these emigrant women. If they still have anything they owed the idolators, then they should return it to them.