אִם־רָעָ֞ה בְּעֵינֵ֧י אֲדֹנֶ֛יהָ אֲשֶׁר־לא [ל֥וֹ] יְעָדָ֖הּ וְהֶפְדָּ֑הּ לְעַ֥ם נָכְרִ֛י לֹא־יִמְשֹׁ֥ל לְמָכְרָ֖הּ בְּבִגְדוֹ־בָֽהּ׃
她的主人本應選定她歸自己為妻，她若不得主人的喜悅，主人就要讓她被贖出去；他既已背信待她，就無權把她賣給外人。
Sefer HaMitzvot
That is that He commanded us to redeem the Hebrew maidservant. And that is His, may He be blessed, saying, "he must let her be redeemed" (Exodus 21:8). This redemption has many analyses and conditions and there are many regulations for it - and they have been explained in Tractate Kiddushin. And the law of the Hebrew maidservant is completely explained there. And in the Mekhilta (Mekhilta d'Rabbi Yishmael 21:11:1) they said in explanation of, "And if these three he does not do to her" (Exodus 21:11), "Designate (marry) [her] yourself, to your son, or redeem her." (See Parashat Mishpatim; Mishneh Torah, Slaves 14.)