Leviticus 16:2, 12-14

and Jehovah said unto Moses, Speak unto Aaron thy brother, that he come not at all times into the holy place within the veil, before the mercy-seat which is upon the ark; that he die not: for I will appear in the cloud upon the mercy-seat.

And he shall take a censer full of coals of fire from off the altar before Jehovah, and his hands full of sweet incense beaten small, and bring it within the veil: and he shall put the incense upon the fire before Jehovah, that the cloud of the incense may cover the mercy-seat that is upon the testimony, that he die not: and he shall take of the blood of the bullock, and sprinkle it with his finger upon the mercy-seat on the east; and before the mercy-seat shall he sprinkle of the blood with his finger seven times.