Deuteronomy 10:2

10:2 I will write on the tablets the same words that were on the first tablets you broke, and you must put them into the ark.”

Exodus 25:16

25:16 You are to put into the ark the testimony that I will give to you.

Exodus 40:20

40:20 He took the testimony and put it in the ark, attached the poles to the ark, and then put the atonement lid on the ark.