If the instrument is one which the law requires should be denied under oath, the affidavit, produced before or at the trial, shall be sufficient to establish the claimant's right, whether such claimant is plaintiff or defendant; and if denied under oath, or otherwise legally put in issue, may be established by competent evidence of its contents.
Code 1858, § 3903 (deriv. Acts 1819, ch. 27, §§ 1, 3, 4); Shan., § 5696; Code 1932, § 9881; T.C.A. (orig. ed.), § 24-803.