11. The matter may be looked at from another point of view. The giving of finger impression or of specimen signature or of handwriting, strictly speaking, is not “to be a witness”. “To be a witness” means imparting knowledge in respect of relevant facts, by means of oral statements or statements in writing, by a person who has personal knowledge of the facts to be communicated to a court or to a person holding an enquiry or investigation. A person is said “to be a witness” to a certain state of facts which has to be determined by a court or authority authorised to come to a decision, by testifying to what he has seen, or something he has heard which is capable of being heard and is not hit by the rule excluding hearsay, or giving his opinion, as an expert, in respect of matters in controversy. Evidence has been classified by text writers into three categories, namely, (1) oral testimony; (2) evidence furnished by documents; and (3) material evidence. We have already indicated that we are in agreement with the Full Court decision in Sharma case [(1954) SCR 1077] that the prohibition in clause (3) of Article 20 covers not only oral testimony given by a person accused of an offence but also his written statements which may have a bearing on the controversy with reference to the charge against him. The accused may have documentary evidence in his possession which may throw some light on the controversy. If it is a document which is not his statement conveying his personal knowledge relating to the charge against him, he may be called upon by the Court to produce that document in accordance with the provisions of Section 139 of the Evidence Act, which, in terms, provides that a person may be summoned to produce a document in his possession or power and that he does not become a witness by the mere fact that he has produced it; and