It was narrated from Ibn 'Abbas that:

a woman came to the Prophet (ﷺ) and became Muslim, and a man married her. Then her first husband came and said: "O Messenger of Allah, I became Muslim with her, and she knew that I was Muslim." So the Messenger of Allah took her away from her second husband and returned her to her first husband.

حَدَّثَنَا أَحْمَدُ بْنُ عَبْدَةَ، حَدَّثَنَا حَفْصُ بْنُ جُمَيْعٍ، حَدَّثَنَا سِمَاكٌ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ امْرَأَةً، جَاءَتْ إِلَى النَّبِيِّ ـ صلى الله عليه وسلم ـ فَأَسْلَمَتْ ‏.‏ فَتَزَوَّجَهَا رَجُلٌ ‏.‏ قَالَ فَجَاءَ زَوْجُهَا الأَوَّلُ فَقَالَ يَا رَسُولَ اللَّهِ إِنِّي قَدْ كُنْتُ أَسْلَمْتُ مَعَهَا وَعَلِمَتْ بِإِسْلاَمِي ‏.‏ قَالَ فَانْتَزَعَهَا رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ مِنْ زَوْجِهَا الآخَرِ وَرَدَّهَا إِلَى زَوْجِهَا الأَوَّلِ ‏.‏