(5)Nothing contained in this section shall apply unless option is exercised by the person in such manner as may be prescribed on or before the due date specified under sub-section (1) of section 139 for furnishing the return of income for any previous year relevant to the assessment year commencing on or after the 1st day of April, 2021 and such option once exercised shall apply to subsequent assessment years:Provided that once the option has been exercised for any previous year, it cannot be subsequently withdrawn for the same or any other previous year.'.
