Exodus 26:34

You shall put the mercy seat on the ark of the Testimony in the Holy of Holies.

Exodus 25:21

You shall put the mercy seat on the top of the ark, and in the ark you shall put the Testimony which I will give you.

Exodus 40:20

He took the Testimony [the stones inscribed with the Ten Commandments] and put it into the ark [of the covenant], and placed the poles [through the rings] on the ark, and put the mercy seat on top of the ark.

Hebrews 9:5

and above the ark were the [golden] cherubim of glory overshadowing the mercy seat; but we cannot now go into detail about these things.

Treasury of Scripture Knowledge

Summary

And thou shalt put the mercy seat upon the ark of the testimony in the most holy place.

General references

Bible References

Put the mercy seat

Exodus 25:21
You shall put the mercy seat on the top of the ark, and in the ark you shall put the Testimony which I will give you.
Exodus 40:20
He took the Testimony [the stones inscribed with the Ten Commandments] and put it into the ark [of the covenant], and placed the poles [through the rings] on the ark, and put the mercy seat on top of the ark.
Hebrews 9:5
and above the ark were the [golden] cherubim of glory overshadowing the mercy seat; but we cannot now go into detail about these things.

General references

Exodus 40:3
You shall place the ark of the Testimony there, and you shall screen off the ark [from the Holy Place of God’s Presence] with the veil (partition curtain).
Mark 15:38
And the veil [of the Holy of Holies] of the temple was torn in two from top to bottom.