Midrash sur L’Exode 21:2

1) (Vayikra 25:39) ("And if your brother grows poor with you, and he is sold to you, do not work with him the work of a servant.") Whence is it derived that one is not permitted to sell himself and place (the proceeds) in his money-bag to buy animals, vessels, or a house unless he became impoverished? From "And if your brother grows poor and he is sold" — He may not sell himself unless he becomes poor. And whence is it derived that when he is sold, he shall be sold only to you (and not to a gentile)? From "and he is sold to you." And whence is it derived that if beth-din sell him they sell him only to you? From (Devarim 15:12) "If there be sold to you." "your brother": You shall treat him as a brother. I might think that he should conduct himself as a brother; it is, therefore, written "a servant." I might think that you shall also conduct yourself to him as a servant; it is, therefore, written "your brother." How so? You conduct yourself to him with brotherhood (i.e., you call him "brother"); he conducts himself to you with servitude (he calls you "master").

R. Simeon the son of Lakish maintained: Shem’s descendants also became slaves, as it is said: And if thy brother, a Hebrew man or a Hebrew woman, be sold unto thee (Deut. 15:12). Shem’s descendants, however, are freed at the expiration of six years, of servitude, as it is written: Then in the seventh year thou shalt let him go free (ibid.), while the descendants of Ham are never freed, as is said: You may hold them to service forever (Lev. 25:46). Therefore, he remains a lifelong slave and does not go forth into the world a free man. Why was this curse imposed upon him? Because he was responsible for his father’s degradation. Thus, the Holy One, blessed be He, brought retribution upon the descendants of Ham by humiliating them by means of the king of Asshur, as it is said: So shall the king of Assyria lead away the captives of Egypt and the exiles of Ethiopia, young and old, naked and barefoot (Isa. 20:4).

(Ibid. 12) "If there be sold, to you, etc.": Whence is it derived that if you buy (a servant), you should buy only a Hebrew servant? From (Shemoth 21:2) "When you buy a Hebrew man-servant." Whence is it derived that if he sells himself, he should sell himself only to you? From (Vayikra 25:39) "And if your brother grows poor with you and he is sold to you…" Whence is it derived that if beth-din sells him, he is sold only to you? From (Ibid. 12) "If there be sold to you (by beth-din, for his theft) your brother …"

"then he shall serve you": — and not your heir. I might think, not even your son; it is, therefore, written (Shemoth 21:2) "Six years shall he serve" (implying that he does serve your son). And why do you see fit to include the son and to exclude the heir (i.e., the daughter)? I include the son for he stands in place of his father for yeidah (living with his father's handmaid), and for (acquiring his) field of holding (viz. Vayikra 25:25), and I exclude the daughter, who does not.