Sifrei_mitzvot for Numbers 29:5

וּשְׂעִיר־עִזִּ֥ים אֶחָ֖ד חַטָּ֑את לְכַפֵּ֖ר עֲלֵיכֶֽם׃

and one he-goat for a sin-offering, to make atonement for you;