Leviticus 16:2; Leviticus 16:15

2 The LORD said to Moses: "Tell your brother Aaron that he shall not enter at any time into the holy place inside the veil, before the mercy seat which is on the ark, or he will die; for I will appear in the cloud over the mercy seat.

15 "Then he shall slaughter the goat of the sin offering which is for the people, and bring its blood inside the veil and do with its blood as he did with the blood of the bull, and sprinkle it on the mercy seat and in front of the mercy seat.