Exodus 39:35

the ark of the testimony and its poles and the atonement cover;

Exodus 25:17

"And you will make an atonement cover of pure gold, two and a half cubits its length and a cubit and a half its width.

Hebrews 9:5

And above it [were] the cherubim of glory overshadowing the mercy seat, about which it is not now [possible] to speak in detail.

Hebrews 9:8

The Holy Spirit [was] making this clear, [that] the way [into] the holy place [was] not yet revealed, [while] the first tent was still in existence,

Treasury of Scripture Knowledge

Summary

The ark of the testimony, and the staves thereof, and the mercy seat,

The mercy seat

Bible References

The mercy seat

Exodus 25:17
"And you will make an atonement cover of pure gold, two and a half cubits its length and a cubit and a half its width.
Hebrews 9:5
And above it [were] the cherubim of glory overshadowing the mercy seat, about which it is not now [possible] to speak in detail.