Leviticus 16:2, 12-14

and the LORD said to Moses, “Tell Aaron your brother not to come at any time into the Holy Place inside the veil, before the mercy seat that is on the ark, so that he may not die. For I will appear in the cloud over the mercy seat.

And he shall take a censer full of coals of fire from the altar before the LORD, and two handfuls of sweet incense beaten small, and he shall bring it inside the veil and put the incense on the fire before the LORD, that the cloud of the incense may cover the mercy seat that is over the testimony, so that he does not die. And he shall take some of the blood of the bull and sprinkle it with his finger on the front of the mercy seat on the east side, and in front of the mercy seat he shall sprinkle some of the blood with his finger seven times.