Leviticus 16:2

16:2 and the Lord said to Moses: “Tell Aaron your brother that he must not enter at any time into the holy place inside the veil-canopy in front of the atonement plate that is on the ark so that he may not die, for I will appear in the cloud over the atonement plate.

Leviticus 16:12-14

16:12 and take a censer full of coals of fire from the altar before the Lord and a full double handful of finely ground fragrant incense, and bring them inside the veil-canopy. 16:13 He must then put the incense on the fire before the Lord, and the cloud of incense will cover the atonement plate which is above the ark of the testimony, so that he will not die. 16:14 Then he is to take some of the blood of the bull and sprinkle it with his finger on the eastern face of the atonement plate, and in front of the atonement plate he is to sprinkle some of the blood seven times with his finger.