Ketubot 37A

וסבר רבי יהודה בקדושתה קיימא? והתניא: הגיורת שנתגיירה וראתה דם, רבי יהודה אומר: דיה שעתה. רבי יוסי אומר: הרי היא ככל הנשים, ומטמאה מעת לעת, ומפקידה לפקידה.

And does R' Yehuda maintain that a captive woman remains in her state of sanctity? But isn’t it taught in a baraita: With regard to a female convert who converted and saw the flow of menstrual blood on that same day, R' Yehuda says: Deeming her impure from the hour that she saw the menstrual flow is sufficient for her. There is no decree of retroactive impurity on objects that she touched earlier, due to the concern that the blood flow might have started earlier. R' Yosei says: Her legal status is like that of all of the Jewish women, and she therefore transmits impurity retroactively for a 24 hour period following her conversion, or from examination to examination, i.e., from the last time she examined herself.

וצריכה להמתין שלשה חדשים, דברי רבי יהודה. רבי יוסי מתיר ליארס ולינשא מיד. אמר ליה: גיורת אשבויה קא רמית? גיורת לא מנטרא נפשה, שבויה מנטרא נפשה.

And a convert is required to wait 3 months after her conversion before marrying a Jew, due to the concern that she is pregnant, leading to confusion whether the child was conceived before or after her conversion; this is the statement of R' Yehuda. R' Yosei permits her to be betrothed and to be married immediately. Clearly, R' Yehuda is concerned that she had sex prior to her conversion. Rav Yosef said to Rav Pappa bar Shmuel: Are you raising a contradiction from the halakha of a convert to that of a captive woman? A convert does not protect herself from having sex before conversion, whereas a captive protects herself, as she is conscious of the sanctity of the Jewish people and does not want to be violated.