Exodus 30:10

וכפר אהרן AND AARON SHALL MAKE EXPIATION — This refers to the placing of the blood upon the horns of the altar. אחת בשנה ONCE IN THE YEAR — On the Day of Atonement. This is what is said in the section אחרי מות, which describes the sacrificial service on that day, (Leviticus 16:18) “And he shall go out unto the altar that is before the Lord and make an expiation upon it”. חטאת הכפרים SIN-OFFERING OF EXPIATION — These are the bullock and goat of the Day of Atonement which atone for the uncleanness of the Sanctuary and its holy offerings (Shevuot 2b; cf. Rashi on Leviticus 16:11). קדש קדשים [IT IS] MOST HOLY — the altar is sanctified for offering on it these things alone and not for any other sacrificial service.

And Aharon shall sprinkle upon the horns of it once in a year the blood of the sin offering of atonements: once in the year shall he make atonement upon it throughout your generations: it is most holy to the Lord.

וְכִפֶּ֤ר אַהֲרֹן֙ עַל־קַרְנֹתָ֔יו אַחַ֖ת בַּשָּׁנָ֑ה מִדַּ֞ם חַטַּ֣את הַכִּפֻּרִ֗ים אַחַ֤ת בַּשָּׁנָה֙ יְכַפֵּ֤ר עָלָיו֙ לְדֹרֹ֣תֵיכֶ֔ם קֹֽדֶשׁ־קׇדָשִׁ֥ים ה֖וּא לַיהֹוָֽה׃ {פ}