It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) concerning this saying of Allah Almighty, "And do not marry polytheist women until they believe" [Surah al-Baqarah: 221], that the women of the People of the Book were then made an exception. He said: "And the chaste women of the People of the Book before you are also lawful for you" [Surah al-Ma'idah: 5], "when you have given them their dues", meaning give them their bridal dues (mahr); "chaste, not fornicators."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13976