Sayyiduna Anas (may Allah be pleased with him) relates: Abu Talhah (may Allah be pleased with him) proposed marriage to Umm Sulaym (may Allah be pleased with her) before he accepted Islam, and she said: "I do indeed desire you, and a man like you is not turned away, but you are a disbeliever and I am a Muslim woman. If you accept Islam, that will be my dowry (mahr); I will not ask you for anything besides it." So Abu Talhah (may Allah be pleased with him) married her.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21735
It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him); he said: Abu Talhah (may Allah be pleased with him) married Umm Sulaym (may Allah be pleased with her), and the dowry between them was accepting Islam. Umm Sulaym (may Allah be pleased with her) had become a Muslim before Abu Talhah; he proposed marriage to her, whereupon she said: "I have become a Muslim; if you become a Muslim, I will marry you." So he became a Muslim, and the dowry between them was accepting Islam itself.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21736