Deuteronomy 31:26 KJV
Take this book of the law, and put it in the side of the ark of the covenant of the Lord your God, that it may be there for a witness against thee.
Deuteronomy 31:26, King James Version
In context
25 That Moses commanded the Levites, which bare the ark of the covenant of the Lord, saying,
26 Take this book of the law, and put it in the side of the ark of the covenant of the Lord your God, that it may be there for a witness against thee.
27 For I know thy rebellion, and thy stiff neck: behold, while I am yet alive with you this day, ye have been rebellious against the Lord; and how much more after my death?