Leviticus 16:2

And Aaron shall make an atonement upon the horns of it once in a year with the blood of the sin offering of atonements: once in the year shall he make atonement upon it throughout your generations: it is most holy unto the LORD.

Nor yet that he should offer himself often, as the high priest entereth into the holy place every year with blood of others;

And the priests brought in the ark of the covenant of the LORD unto his place, into the oracle of the house, to the most holy place, even under the wings of the cherubims.

So that the priests could not stand to minister by reason of the cloud: for the glory of the LORD had filled the house of God.

And, behold, the veil of the temple was rent in twain from the top to the bottom; and the earth did quake, and the rocks rent;

And after the second veil, the tabernacle which is called the Holiest of all;

And he shall put the incense upon the fire before the LORD, that the cloud of the incense may cover the mercy seat that is upon the testimony, that he die not:

Therefore shall ye abide at the door of the tabernacle of the congregation day and night seven days, and keep the charge of the LORD, that ye die not: for so I am commanded.

Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation unto you; and ye shall afflict your souls, and offer an offering made by fire unto the LORD.

And the LORD said unto Moses, Bring Aaron’s rod again before the testimony, to be kept for a token against the rebels; and thou shalt quite take away their murmurings from me, that they die not.

But thus do unto them, that they may live, and not die, when they approach unto the most holy things: Aaron and his sons shall go in, and appoint them every one to his service and to his burden: