Reference for Ketubot 23:1

אמר רבה זאת אומרת כנסה בחזקת בתולה ונמצאת בעולה יש לה כתובה מנה רב אשי אמר בעלמא לעולם אימא לך לית לה כלל ושאני הכא שהרי כנסה ראשון

Rabbah said: This means that if he married her in the presumption that she was a virgin and she was found to have had intercourse she gets a ketubah of a maneh. Ashi said: In general I could say to you that she receives nothing; but it is different here, because the first one had married her.

Jastrow