A Division bench of Apex Court held as follows,

In the absence of cross-examination of the postman on this crucial aspect his statement in the chief-examination has been rightly relied upon. There is an age old rule that if you dispute the correctness of the statement of a witness you must give him opportunity to explain his statement by drawing his attention to that part of it which is objected to as untrue, otherwise you can not impeach his credit. In State of U.P. v. Nahar Sing (dead) and Ors., [1998] 3 SCC 561, a Bench of this Court (to which 1 was a party) stated the principle that Section 138 of the Evidence Act confers a valuable right to cross-examination a witness tendered in evidence by opposite party. The scope of that provision is enlarged by Section 146 of the Evidence Act by permitting a witness to be questioned, inter alia, to test his veracity. It was observed.
“The oft-quoted observation of Lord Herschell, L.C. in Browne v. Dunn clearly elucidates the principle underlying those provisions. It reads thus:
“I cannot help saying, that it seems to me to be absolutely essential to the proper conduct of a cause, where it is intended to suggest that a witness is not speaking the truth on a particular point, to direct his attention to the fact by some questions put in cross-examination showing that that imputation is intended to be made and not to take his evidence and pass it by as a matter altogether unchallenged, and then, when it is impossible for him to explain, as perhaps he might have been able to do if such questions had been put to him, the circumstances which, it is suggested, indicate that the story he tells ought not to be believed, to argue that he is a witness unworthy of credit. My Lords, I have always understood that if you intend to impeach a witness, you are bound, whilst he is in the box, to give an opportunity of making any explanation which is open to him; and, as it seems to me, that is not only a rule of professional practice in the conduct of a case, but it is essential to fair play and fair dealing with witnesses.”

Citations : [2001 AIR SC 3042], [2001 SCALE 5 203], [2001 SUPREME 6 82], [2001 AIR SC 3207], [2001 SCC 7 69], [2002 UJ SC 1 89], [2001 DLT SC 93 1], [2001 UC 2 415], [2001 ALR 44 843], [2002 LW 1 69], [2001 AIR SCW 3042], [2001 JT SC 6 400]

Other Sources :

https://indiankanoon.org/doc/1624346/

https://www.casemine.com/judgement/in/5609ad98e4b0149711411cf1