Mishkat al-Masabih 13 Marriage كتاب النكاح 127

وَعَنْ أَنَسٍ قَالَ: تَزَوَّجَ أَبُو طَلْحَةَ أُمَّ سُلَيْمٍ فَكَانَ صَدَاقُ مَا بَيْنَهُمَا الْإِسْلَامَ أَسْلَمَتْ أُمُّ سُلَيْمٍ قَبْلَ أَبِي طَلْحَةَ فَخَطَبَهَا فَقَالَتْ: إِنِّي قَدْ أَسْلَمْتُ فَإِنْ أَسْلَمْتَ نَكَحْتُكَ فَأَسْلَمَ فَكَانَ صدَاق مَا بَينهمَا. رَوَاهُ النَّسَائِيّ

Anas said that Abu Talha married Umm Sulaim, the dower between them being acceptance of Islam. Umm Sulaim had become a Muslim before Abu Talha, and when he asked her in marriage she said, “I have become a Muslim, so if you become one I shall marry you.” He then accepted Islam and that was the dower arranged between them. Nasa’i transmitted it.