Kiddushin 45A

ושוין שמוכרה אלמנה לכהן גדול, גרושה וחלוצה לכהן הדיוט. האי אלמנה היכי דמי? אילימא דקדשה אביה, מי מצי מזבין לה? הא אין אדם מוכר את בתו לשפחות אחר אישות! אלא לאו דקדיש איהי נפשה וקא קרי לה אלמנה!

And they agree that he can sell her to a High Priest even if she is a widow, or to a common priest even if she is a divorcée or is a yevama who performed ḥalitza [ḥalutza]. Although such marriages are prohibited, they do take effect. The Talmud analyzes this: What are the circumstances of this widow who can be sold as a female slave by her father? If we say that her father betrothed her and her husband subsequently died while she was still a minor, is he able to sell her after her betrothal? A person cannot sell his daughter into servitude after he has betrothed her. Rather, isn’t the baraita referring to a case when she betrothed herself as a minor, and yet it calls her a widow, indicating that such a betrothal is effective, contrary to the opinion of Ulla.

אמר רב עמרם אמר רבי יצחק: הכא בקידושי יעוד. ואליבא דרבי יוסי ברבי יהודה, דאמר: מעות הראשונות לאו לקידושין ניתנו.

Rav Amram said that R' Yitzḥak said: Here it deals with a minor girl widowed from a betrothal of designation, i.e., her father sold her as a Hebrew female slave, and the master designated her as his wife but died before he married her. And this is in accordance with the opinion of R' Yosei, son of R' Yehuda, who says: The original money of the sale of the female slave was not given for the purpose of betrothal. Rather, her betrothal goes into effect when her master relinquishes his rights to have her serve as a Hebrew female slave. Since this betrothal was not accepted by the father, he is later permitted to sell her as a female slave again.