Exodus 26:34

You are to put the cover on the ark of the law, inside the most holy place.

Exodus 25:21

And put the cover over the ark, and in the ark the record which I will give you.

Exodus 40:20

And he took the law and put it inside the ark, and put the rods at its side and the cover over it;

Hebrews 9:5

And over it were the winged ones of glory with their wings covering the mercy-seat; about which it is not possible now to say anything in detail.

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
And put the cover over the ark, and in the ark the record which I will give you.
Exodus 40:20
And he took the law and put it inside the ark, and put the rods at its side and the cover over it;
Hebrews 9:5
And over it were the winged ones of glory with their wings covering the mercy-seat; about which it is not possible now to say anything in detail.

General references

Exodus 40:3
And inside it put the ark of the law, hanging the veil before it.
Mark 15:38
And the curtain of the Temple was parted in two from end to end.

Basic English, produced by Mr C. K. Ogden of the Orthological Institute - public domain