Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 50
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 50, with English translation by Maimonides (Rambam).
להוסיף קרבן בחג הסוכות, שנאמר: "וְהִקְרַבְתֶּם עוֹלָה אִשֵּׁה רֵיחַ נִיחוֹחַ" (במדבר כט, יג).
To offer an additional sacrifice on the holiday of Sukkot, as [Numbers 29:13] states: "And you shall present a burnt offering as a pleasing fragrance...."