A pleading setting up any of the following matters, unless the truth of such matters appear of record, shall be verified by affidavit.
A denial of any of the matters set forth in subdivisions (a) or (g) of paragraph 13 may be made on information and belief.
Any such denial may be made in original or amended pleadings; but if in amended pleadings the same must be filed not less than seven days before the case proceeds to trial. In case of such denial the things so denied shall not be presumed to be true, and if essential to the case of the party alleging them, must be proved.
Tex. R. Civ. P. 93