וְהִקְרִ֧יב אַהֲרֹ֛ן אֶת־פַּ֥ר הַחַטָּ֖את אֲשֶׁר־ל֑וֹ וְכִפֶּ֥ר בַּעֲד֖וֹ וּבְעַ֥ד בֵּיתֽוֹ׃
Aaron bringe dann seinen Farren der Sühne dar, und sühne sich und sein Haus.
Rashi on Leviticus
את פרי החטאת אשר לו [AND AARON SHALL OFFER] THE BULL OF SIN OFFERING WHICH IS HIS — i. e. that mentioned above (v. 3). It teaches you here, by adding the words אשר לו, that it came (had to be purchased) from his own and not from the money of the community (Sifra, Acharei Mot, Section 2 2; Yoma 3b).
Siftei Chakhamim
And not from public [funds]. Rashi is answering the question: Why does it say “which is his,” if no other bull is mentioned in this parsha except that of Aharon as it is written, “With this Aharon shall come... with a young bullock?” [He answers]: This indicates that he must bring the sacrifices from his [property]. In addition, since it is written above, “He shall take, from the congregation of Israel two he-goats etc.,” it indicates that the sacrifices written above he brought for himself [i.e., with his own funds].