Her Dowry Was Islaam

Anas said: "Abu Talhah proposed to Umm Sulaim and she said, 'It is not fitting that I should marry a polytheist. Don't you know, O Aba Talhah, that your gods are carved by the slave of such and such family? And were you to ignite a fire under it, it will burn?' He left while that was registered on his mind. Thereafter he came to her and said, 'I have accepted what you have presented to me.' He said, 'She did not have any mahr other than Islaam.'" [Sahih, At-Tabaqat]

In another narration by An-Nasai from Anas, who said: Abu Talhah proposed to Umm Sulaim and she said, "By Allaah, someone like you is not to be rejected, O Aba Talhah, but you are a polytheist while I am a Muslim woman. It is not permissible for me to marry you but if you accept Islaam, then that will be my dowry, I do not ask you for other than that." So he became Muslim and that was her mahr. 

Thaabit said, "I never heard of any woman who had a more noble mahr than Umm Sulaim. He consummated the marriage with her and she bore him children."

MaashaaAllaah! May Allaah be pleased with them both!