Behar, Chapter 7
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").