The commandment of the additional sacrifice on the day of the festival of Shavuot: That Israel was commanded to sacrifice an additional sacrifice on the day of the festival of Shavuot, as it is stated (Numbers 28:26), “And on the day of the first-fruits when you bring a new meal-offering to the Lord on your festival of Weeks (Shavuot), etc.” And I have already written twice that I have spoken about the matter of the additional sacrifices in the Order of Emor el HaKohanim regarding the addition of Pesach (Sefer HaChinukh 299).
מִצְוַת קָרְבַּן מוּסָף בְּיוֹם חַג הַשָּׁבוּעוֹת – שֶׁנִּצְטַוּוּ יִשְׂרָאֵל לְהַקְרִיב קָרְבַּן מוּסָף בְּיוֹם חַג הַשָּׁבוּעוֹת, שֶׁהוּא יוֹם שִׁשִּׁי בְּסִיוָן, שֶׁנֶּאֱמַר (במדבר כח כו) וּבְיוֹם הַבִּכּוּרִים בְּהַקְרִיבְכֶם מִנְחָה חֲדָשָׁה לַיְיָ בְּשָׁבֻעֹתֵיכֶם וְגוֹ'. כְּבָר כָּתַבְתִּי פַּעֲמַיִם, כִּי בְּסֵדֶר אֱמֹר אֶל הַכֹּהֲנִים בְּמוּסָף דְּפֶסַח (מצוה רצט), דִּבַּרְתִּי מֵעִנְיַן הַמּוּסָפִין.
The commandment of the additional sacrifice on the day of the festival of Shavuot: That Israel was commanded to sacrifice an additional sacrifice on the day of the festival of Shavuot, as it is stated (Numbers 28:26), “And on the day of the first-fruits when you bring a new meal-offering to the Lord on your festival of Weeks (Shavuot), etc.” And I have already written twice that I have spoken about the matter of the additional sacrifices in the Order of Emor el HaKohanim regarding the addition of Pesach (Sefer HaChinukh 299).