וְזָ֣כַרְתָּ֔ כִּי־עֶ֥בֶד הָיִ֖יתָ בְּמִצְרָ֑יִם וְשָׁמַרְתָּ֣ וְעָשִׂ֔יתָ אֶת־הַֽחֻקִּ֖ים הָאֵֽלֶּה׃ (פ)
And thou shalt remember that thou wast a bondman in Egypt; and thou shalt observe and do these statutes.
Sifrei Devarim
(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).