Explanation:

Section 155 of Evidence Act – 
155. Impeaching credit of witness. –– The credit of a witness may be impeached in the following ways by the adverse party, or, with the consent of the Court, by the party who calls him: –– (1) by the evidence of persons who testify that they, from their knowledge of the witness, believe him to be unworthy of credit; o to give his evidence; (3) by proof of former statements inconsistent with any part of his evidence which is liable to be contradicted; 1 * * * * * Explanation. –– A witness declaring another witness to be unworthy of credit may not, upon his examination-in-chief, give reasons for his belief, but he may be asked his reasons in cross-examination, and the answers which he gives cannot be contradicted, though, if they are false, he may afterwards be charged with giving false evidence.