Leviticus 16:2, 12-14

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 take a censer full of burning coals of fire from the altar before the LORD, with his hands full of sweet incense beaten fine, and bring it inside the veil. And he shall put the incense on the fire before the LORD, that the cloud of incense may cover the mercy seat that is on the Testimony, lest he die. He shall take some of the blood of the bull and sprinkle it with his finger on the mercy seat on the east side; and before the mercy seat he shall sprinkle some of the blood with his finger seven times.