Midrash sa Exodo 21:8: Mekhilta DeRabbi Yishmael, Mekhilta DeRabbi Shimon Ben Yochai & Bereshit Rabbah

No, this may be true of a Hebrew maid-servant, who is not sold for her theft, wherefore she does not go out with mutilation of organ prominences, (as opposed to a man-servant, who is sold for his theft.) (Exodus 21:8) "If she be evil in the eyes of her master": "evil" here connotes her not finding favor in his eyes."

"who did not designate her (to be his wife), then he shall redeem her": From here they ruled that the mitzvah of marrying her takes precedence to that of his redeeming her.

"If she is displeasing" – I have only [the case where she is] ugly. From where [do I know this applies to one who is] beautiful? Scripture teaches: "in the eyes of her master." "In the eyes of his son" – from where? Scripture teaches: "displeasing." Rabbi Eliezer says: "If she is displeasing in the eyes of her master" – to include those who are disqualified [from marrying her]. "Who has not designated her" – From the negative implication [we learn] affirmatively: if he wishes to designate her, he may designate her. "He shall designate her" – With her consent. This teaches that he only betroths her with her consent. And the same law applies to all women – they are only betrothed with their consent and willingness. Is this not a kal vachomer? If a Hebrew maidservant, who is subjugated under his hand, the Torah says he shall designate her with her consent – other women, all the more so! How does he designate her? He says to her in the presence of two [witnesses]: "Behold, you are betrothed to me," and he does not need to give her kiddushin [betrothal money]. Another interpretation: "He shall designate her" – teaches that he cannot designate two [maidservants] at once. "He shall designate her" and "she shall be redeemed" – teaches that the commandment of designation precedes the commandment of redemption. "And she shall be redeemed" – teaches that she goes free through a deduction of money. Another interpretation: "And she shall be redeemed" – teaches that the court redeems her against his will. Another interpretation: "He shall designate her" and "she shall be redeemed" – there is designation only during the time of redemption. For if he designated her within six [years], even at [the payment of] the last perutah, this is a [valid] designation. But if he designated her after six [years], there is no designation here. "To a foreign people he shall not sell" – One might think he shall not sell her but may give her as a gift? Scripture teaches: "he shall not have power." One might think he shall not sell her to strangers but may sell her to relatives? Scripture teaches: "to a people he shall not sell." One might think he shall not sell her but may give her as a gift? Scripture teaches: "to a people he shall not have power." If it says "to strangers," why do I need it to say "to relatives"? For if it said "to strangers" and not "to relatives," I would say he shall not sell her to strangers but may sell her to relatives. If it says "to relatives," [why do I need it to say "to strangers"? For if it said "to relatives" and not "to strangers," I would say] he shall not sell her to relatives who are forbidden to her [in marriage], but may sell her to strangers who are permitted to her. Therefore it is necessary to say both "to strangers" and "to relatives." I have only [the prohibition regarding] a Hebrew maidservant. From where [do I derive the same for] a Hebrew slave? You derive it through a kal vachomer: If a Hebrew maidservant, whom he is permitted to designate for himself and for his son, he is not permitted to sell her [to a non-Jew] – a Hebrew slave, over whom he has no [marital] authority at all, all the more so! And if he sold [him], he has accomplished nothing, but he does not receive lashes. "In his betraying her" – Once he has spread his garment over her [consummated marriage], he cannot sell her. Another interpretation: "He shall not have power to sell her – in his betraying her." Rabbi Shimon says: [Regarding] the first one who betrayed her and divorced her – you are not permitted to enslave her. From here they said: A person does not sell his daughter into servitude after [she has been married as] wives.