Abu Talha married Umm Sulaym, and the dowry between them was Islam. Umm Sulaym had embraced Islam before Abu Talha. He proposed to her, and she said, "I have embraced Islam. If you embrace Islam, I will marry you." So he embraced Islam, and that was the dowry between them.
أخبرنا قتيبة قال حدثنا محمد بن موسى عن عبد الله بن عبد الله بن أبي طلحة
تزوج أبو طلحة أم سليم فكان صداق ما بينهما الإسلام أسلمت أم سليم قبل أبي طلحة فخطبها فقالت إني قد أسلمت فإن أسلمت نكحتك فأسلم فكان صداق ما بينهما
No references are available.
Its isnad is sahih. Ibn Saad narrated it in 8/426 from the hadith of Muhammad bin Musa Fitri, through him, and it is in Kubra, hadith no. 5503.