Exodus 30:10

30:10 Aaron is to make atonement on its horns once in the year with some of the blood of the sin offering for atonement; ¹  once in the year ²  he is to make atonement on it throughout your generations. It is most holy to the Lord.” ³ 

[30:10]  ¹ tn The word “atonements” (plural in Hebrew) is a genitive showing the result or product of the sacrifice made.

[30:10]  ² sn This ruling presupposes that the instruction for the Day of Atonement has been given, or at the very least, is to be given shortly. That is the one day of the year that all sin and all ritual impurity would be removed.

[30:10]  ³ sn The phrase “most holy to the Lord” means that the altar cannot be used for any other purpose than what is stated here.