Article 41 of Law of Evidence

Proof by witness testimony may be admitted in matters required to be proved in writing in the following cases: First: Where there is a commencement of proof in writing. Any writing emanating from the opposing litigant that renders the existence of the alleged legal transaction probable shall constitute a commencement of proof in writing. Second: Where a material or moral impediment prevents obtaining written evidence. Third: Where the creditor has lost the written instrument owing to an external cause beyond the creditor's control.