Leviticus 16:2, 15

and the LORD said to Moses: “Tell Aaron your brother not to come at just any time into the Holy Place inside the veil, before the mercy seat which is on the ark, lest he die; for I will appear in the cloud above the mercy seat.

“Then he shall kill the goat of the sin offering, which is for the people, bring its blood inside the veil, do with that blood as he did with the blood of the bull, and sprinkle it on the mercy seat and before the mercy seat.