Leviticus 16:2, 12-14

The LORD said to Moses: “Tell your brother Aaron that he is not to come whenever he chooses into the Most Holy Place behind the curtain in front of the atonement cover on the ark, or else he will die. For I will appear in the cloud over the atonement cover.

He is to take a censer full of burning coals from the altar before the LORD and two handfuls of finely ground fragrant incense and take them behind the curtain. He is to put the incense on the fire before the LORD, and the smoke of the incense will conceal the atonement cover above the tablets of the covenant law, so that he will not die. He is to take some of the bull’s blood and with his finger sprinkle it on the front of the atonement cover; then he shall sprinkle some of it with his finger seven times before the atonement cover.