Deuteronómio 16:12 Midrash: Mekhilta DeRabbi Yishmael & Sifrei Devarim

(Ibid.) "If you buy (lit.,) a servant Hebrew": Is Scripture speaking of a servant who is a Hebrew, or the servant of a Hebrew? And how am I to understand (Leviticus 25:46) "And you shall hold them as an inheritance for your sons after you, etc."? As referring to (a gentile servant) bought from a gentile; but if he were bought from a Jew, (I would say that) he serves six years and goes free on the seventh. It is, therefore, written (Devarim 15:12) "If there be sold to you (by beth-din for his theft) your brother, the Hebrew man or the Hebrew woman, etc." Let it not be written "Hebrew man" or "Hebrew woman," for it is already written "your brother."

(Devarim 16:12) "And you shall remember that you were a slave in the land of Egypt, and you shall take heed and observe these statutes": This teaches us that all (the obligations of rejoicing) which obtain on Atzereth (Shavuoth) obtain on Pesach and Succoth, (these, too, commemorating the exodus from Egypt.) — But perhaps all that obtains on Pesach and Succoth (e.g., matzoth, lulav, etc.) also obtain on Atzereth! It is, therefore, written "these statutes." These obtain on Atzereth, but not matzoh, succah, lulav, and seven (days).