Evidence as to matters in writing
146.  Any witness may be asked while under examination whether any contract, grant or other disposition of property as to which the witness is giving evidence was not contained in a document, and if the witness says that it was, or if the witness is about to make any statement as to the contents of any document which in the opinion of the court ought to be produced, the adverse party may object to such evidence being given until such document is produced or until facts have been proved which entitle the party who called the witness to give secondary evidence of it.
     Explanation.—A witness may give oral evidence of statements made by other persons about the contents of documents if such statements are in themselves relevant facts.
Illustration
     The question is whether A assaulted B.
     C deposes that he or she heard A say to D: “B wrote a letter accusing me of theft and I will be revenged on him”. The statement is relevant as showing A’s motive for the assault and evidence may be given of it though no other evidence is given about the letter.