Saffiyah Mother of the believers, may Allah be pleased with her was from the children of Israel and a Muslim who was once following the way of the Jews.
Aiesha who was also one of the mothers of the believers was once reprimanded by the Prophet for calling Saffiya a Jewess.
As you can clearly see, it was her faith that changed and NOT her ETHNICITY!
Read and take heed for you not to fall into the same error, as their are no excuses for falling into this error!
سير اعلام النبلا ج 2 ص 122
وعن عطاء بن يسار ، قال : لما قدم رسول الله من خيبر ، ومعه صفية ، أنزلها ، فسمع بجمالها نساء الأنصار ، فجئن ينظرن إليها ، وكانت عائشة متنقبة حتى دخلت ، فعرفها ، فلما خرجت ، خرج ، فقال : كيف رأيت ؟ قالت : رأيت يهودية . قال : لا تقولي هذا ، فقد أسلمت
On the authority of Ata Ibn Yasaar, He said, When the Messenger of Allah entered Khaibar, he was with Safiyyah and he entered her, and the woman of the Ansar heard about her beauty. So they came to look at her. And Aiesha was veiled until she entered, then she raised it (her veil). Then when she exited, he (The Prophet) exited and he said , What do think? She said, I saw A Jewish woman and he said ”D0 NOT SAY THIS, for verily she has become a Muslima!”