Midrash sa Exodo 21:9: Mekhilta DeRabbi Yishmael

"After he (the father) has been faithless ("bagdah") to her" (by selling her,) by degrading her and not treating her as a Jewish daughter, he, too, is not permitted to retain her (i.e., to sell her a second time). These are the words of R. Yonathan b. Avtalmos. "bagdah" here connotes deceit" as in (Malachi 2:11) "bagdah Yehudah" and (Jeremiah 5:11) "for the house of Israel bagod bagdu against Me."

(Exodus, Ibid. 9) "And if to his son he designate her (as a wife)": He designates her to his son, but not to his brother. For it would follow (that he does designate her to his brother), viz.: If he designates his son, who does not take his place through yibum (levirate marriage), how much more so, his brother, who does take his place through yibum! — No, this may be true of his son, who takes his place vis-à-vis (reversion to his father of) a (field of) holding (on the Yovel), (as opposed to his brother, who does not.) It is, therefore, written "And if to his son he designate her" — to his son and not to his brother.

R. Yonathan says: Scripture (in "he shall not withhold") speaks of a Jewess (in general). You say it speaks of a Jewess, but perhaps it speaks of the Hebrew maid-servant. — (No, for [9]) "according to the ordinance of the daughters shall he provide for her" already speaks of the Hebrew maid-servant. How, then, am I to understand "If another he take for himself"? As applying to a Jewess (in general).