The Quran

يا أَيُّهَا الَّذينَ آمَنوا إِذا جاءَكُمُ المُؤمِناتُ مُهاجِراتٍ فَامتَحِنوهُنَّ ۖ اللَّهُ أَعلَمُ بِإيمانِهِنَّ ۖ فَإِن عَلِمتُموهُنَّ مُؤمِناتٍ فَلا تَرجِعوهُنَّ إِلَى الكُفّارِ ۖ لا هُنَّ حِلٌّ لَهُم وَلا هُم يَحِلّونَ لَهُنَّ ۖ وَآتوهُم ما أَنفَقوا ۚ وَلا جُناحَ عَلَيكُم أَن تَنكِحوهُنَّ إِذا آتَيتُموهُنَّ أُجورَهُنَّ ۚ وَلا تُمسِكوا بِعِصَمِ الكَوافِرِ وَاسأَلوا ما أَنفَقتُم وَليَسأَلوا ما أَنفَقوا ۚ ذٰلِكُم حُكمُ اللَّهِ ۖ يَحكُمُ بَينَكُم ۚ وَاللَّهُ عَليمٌ حَكيمٌ

Ali Unal

O you who believe! When believing women come to you as emigrants, test them;¹ (though only) God knows best their faith. Then, if you have ascertained that they are believers,² do not return them to the unbelievers. They are not (being believers) lawful (as wives) for the unbelievers, nor are the unbelievers lawful (as husbands) for them. But return to them (the unbelievers) whatever they expended (by way of bridal-due when they wed those women).³ And there will be no blame on you (O believers) if you marry them when you have given them their bridal-due. Also (on the other side), do not continue to retain disbelieving women in marriage, and ask for the return of whatever you expended as their bridal-due (if they remain among the unbelievers oror join them), just as the disbelieving men (whose wives have emigrated to you after embracing Islam) have the right to demand the return of whatever they spent. That is God’s judgment and His law; He lays down the law and judges between you. God is All-Knowing, All-Wise.

Under the terms of the Treaty of Hudaybiyah, people or tribes could join or ally themselves with whomever they wished – to the pagan Quraysh, or the Muslims in Madīnah— and any Makkan men who defected to Madīnah would be returned. The Quraysh took this stipulation to include also married women. So when several Makkan women embraced Islam after the Treaty and emigrated to Madīnah, their return to Makkah was demanded. However, since the word “men” was used in the stipulation mentioned, the Messenger, upon him be peace and blessings, responded that the stipulation included only the men, not the women, and he rejected the demand. This verse is concerned with these women and, of course, encompasses all women who take refuge in a Muslim land claiming that they have become Muslims and who have left their husbands on account of their religion.
In order to establish whether they were believers, they were asked to swear by God. It is clear that this is a procedure of legal form and effect. It is because of this that God reminds us that it is only He who can determine whether they are true believers.
Since a former husband who is not Muslim is not responsible for the breaking of the marriage contract, and it is the (newly Muslim) wife who is considered to be responsible, she has to refund the bridal-due that she received at the time of the marriage contract. If the woman is unable to do that, the Muslim community (or state on behalf of the community) is obliged to indemnify the former husband.