כִּֽי־עֲבָדַ֣י הֵ֔ם אֲשֶׁר־הוֹצֵ֥אתִי אֹתָ֖ם מֵאֶ֣רֶץ מִצְרָ֑יִם לֹ֥א יִמָּכְר֖וּ מִמְכֶּ֥רֶת עָֽבֶד׃
Porque são meus servos, que tirei da terra do Egito; não serão vendidos como escravos.
Rashi on Leviticus
כי עבדי הם FOR THEY ARE MY SERVANTS — My document (deed of purchase) is of an earlier date ( Sifra, Behar, Section 6 1).
Sforno on Leviticus
כי עבדי הם, even though this labourer had “sold” himself to you, thus meaning to acquire a new master, it might have been assumed that you might treat him like a servant instead of like a hired labourer, the fact remains that seeing he was and remains “MY” servant; this is not the way you can treat him. No Jew is legally able to sell his body, seeing that he already “belongs” to G’d.
Rashi on Leviticus
לא ימכרו ממכרת עבד THEY SHALL NOT BE SOLD AS THOUGH BY THE SALE OF A BONDSMAN — by public announcement: “Here is a slave to be sold!” Nor shall one make him stand on the auction-stone (Sifra, Behar, Section 6 1).