Sefer HaMitzvot
That is that He commanded to offer an additional sacrifice on the tenth day of Tishrei. And that is His, may He be blessed, saying, "And on the tenth day of the seventh month [...] You shall offer a burnt-offering as a pleasing odor to the Lord" (Numbers 29:7-8). (See Parashat Pinchas; Mishneh Torah, Daily Offerings and Additional Offerings 10.)