Mo. Rev. Stat. § 490.650: Account book, when produced.

The court before which any action for the recovery of any sum or balance due on account, and where the matter at issue and on trial is a proper and usual subject of charge on books of account, may require either party to produce, at the trial, either his ledger or original book of entries, or both; and no disputed account shall be allowed upon the oath of the party, when it shall appear that he has a book of original entries, unless such book shall be produced upon reasonable request.