Impeaching credit of witness

(1) The credit of any witness may be impeached by the opposite party by the evidence of persons who swear that they, from their knowledge of the witness, believe him to be unworthy of credit upon oath, but those persons may not, upon their examination-in-chief, give reasons for their belief, although they may be asked their reasons in cross-examination and their answers cannot be contradicted. (2) It shall not be competent for the party by whom any witness is called to impeach the credit of that witness by any such evidence but, when it is given by the opposite party, the party who called the witness may give evidence in reply to show that the witness is worthy of credit.