The presumption of legitimacy of a child is defined under:-

Section 112 Indian evidence act - Bih during marriage, conclusive proof of legitimacy. The fact that any person was born. during the continuance of a valid marriage between his mother and any man, or within two hundred and eighty days (280 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 paies to the marriage had no access to each other at any time when he could have been begotten.