The commandment of the additional sacrifice on the day of Rosh Hashanah: To sacrifice the additional sacrifice on the day of Rosh Hashanah, as it is stated (Leviticus 23:24-25), “On the seventh month on the first of the month, etc. and you shall bring a fire-offering to the Lord, etc.” And in the Order of Pinchas (Numbers 29:2-5), it mentions the sacrifice at length. And all of its content is like I wrote about the additional sacrifice of Pesach in the commandment of the additional offering of all of the seven days of Pesach in this Order (Sefer HaChinukh 299).
מִצְוַת קָרְבַּן מוּסָף בְּיוֹם רֹאשׁ הַשָּׁנָה – לְהַקְרִיב קָרְבַּן מוּסָף בְּיוֹם רֹאשׁ הַשָּׁנָה, שֶׁנֶּאֱמַר (ויקרא כג כד כה) וּבַחֹדֶשׁ הַשְּׁבִיעִי בְּאֶחָד לַחֹדֶשׁ וְגוֹ' וְהִקְרַבְתֶּם אִשָּׁה לַיְיָ וְגוֹ' וּבְסֵדֶר פִּנְחָס (במדבר כט ב ה) מַזְכִּיר הַקָּרְבָּן בַּאֲרֻכָּה. וְכָל עִנְיָנָהּ כְּמוֹ שֶׁכָּתַבְתִּי בְּמוּסָף הַפֶּסַח בְּמִצְוַת קָרְבַּן מוּסָף שֶׁל כָּל שִׁבְעַת יְמֵי הַפֶּסַח שֶׁבְּסֵדֶר זֶה (מצוה רצט).
The commandment of the additional sacrifice on the day of Rosh Hashanah: To sacrifice the additional sacrifice on the day of Rosh Hashanah, as it is stated (Leviticus 23:24-25), “On the seventh month on the first of the month, etc. and you shall bring a fire-offering to the Lord, etc.” And in the Order of Pinchas (Numbers 29:2-5), it mentions the sacrifice at length. And all of its content is like I wrote about the additional sacrifice of Pesach in the commandment of the additional offering of all of the seven days of Pesach in this Order (Sefer HaChinukh 299).