מִצְוַת קָרְבַּן מוּסָף שֶׁל יוֹם הַכִּפּוּרִים – לְהַקְרִיב קָרְבַּן מוּסָף בְּיוֹם הַכִּפּוּרִים שֶׁנֶּאֱמַר (ויקרא כג כז) אַךְ בֶּעָשׂוֹר לַחֹדֶשׁ וְגוֹ' וְהִקְרַבְתֶּם אִשָּׁה לַיְיָ. וּבְסֵדֶר פִּנְחָס פֵּרֵשׁ הַקָּרְבָּן כְּמוֹ שֶׁכָּתוּב שָׁם (במדבר כט ח) וְהִקְרַבְתֶּם עֹלָה לַיְיָ רֵיחַ נִיחֹחַ פַּר בֶּן בָּקָר אֶחָד אַיִל אֶחָד כְּבָשִׂים בְּנֵי שָׁנָה שִׁבְעָה וְגוֹ'. וְזֶה הַכָּתוּב שֶׁבְּפִנְחָס, הֵבִיא הָרַמְבַּ"ם זִכְרוֹנוֹ לִבְרָכָה בְּמִנְיָנוֹ (סהמ"צ עשין מח), וַאֲנִי כָּתַבְתִּי הַקּוֹדֵם בַּתּוֹרָה, וְהַכֹּל עוֹלֶה לְעִנְיַן אֶחָד. The commandment of the additional sacrifice of Yom Kippur: To sacrifice the additional sacrifice on Yom Kippur, as it is stated (Leviticus 23:27), “But on the tenth of the month, etc. and you shall sacrifice a fire-offering to the Lord.” And in the Order of Pinchas, the sacrifice is explained, as it is written there (Numbers 29:8), “And you shall sacrifice a burnt-offering to the Lord, a pleasing smell; one young bull, one ram, seven one-year old sheep, etc.” And Rambam, may his memory be blessed, brought this verse that is in Pinchas in his tally (Sefer HaMitzvot, Positive Commandments 48), whereas I have written the one that is first in the Torah. But it all comes to the same thing.
מִשָּׁרְשֵׁי מִצְוַת קָרְבַּן הַמּוּסָף וּקְצָת דִּינָיו, כְּבָר כָּתַבְתִּי מָה שֶׁיָּדַעְתִּי בְּמוּסָף הַפֶּסַח שֶׁבְּסֵדֶר זֶה (מצוה רצט), וְקֶשֶׁר אֶחָד לְכֻלָּם לְפִי הַדּוֹמֶה. I have already written what I have known from the roots of the commandment of the additional sacrifice and some of its laws in the additional sacrifice of Pesach in this Order (Sefer HaChinukh 299). And there is one connection to all of them that are similar.