Indian Evidence Act, 1872
112. Birth during marriage, conclusive proof of legitimacy
The fact that any
person was born during the continuance of a valid marriage between his mother
and man, or within two hundred and eighty days after its dissolution, the
mother remaining unmarried, shall be conclusive proof that he is the legitimate
son of that man, unless it can be shown that the parties to the parties to the
marriage had no access to each other at any time when he could have been
begotten.