Holy of Holies: Contained: Ark of Testimony
Source: TTT
Exodus 26:33
And hang the veil from the clasps and place the ark of the Testimony behind the veil. So the veil will separate the Holy Place from the Most Holy Place.
Exodus 40:3, 21
Put the ark of the Testimony in it and screen off the ark with the veil. / Then he brought the ark into the tabernacle, put up the veil for the screen, and shielded off the ark of the Testimony, just as the LORD had commanded him.