Sec 43B provides that a deduction otherwise allowable in respect of (amongst other things) any sum payable as bonus...shall be allowed (irrespective of the previous year in which the liability to pay such sum was incurred by the assessee according to the method of accounting regularly employed by him) only in computing the income referred to in section 28 of that previous year in which sum is actually paid by him.
Provided that nothing contained in this section shall apply in relation to any sum referred to in clause (a) or clause (c) or clause (d) or clause (e) which is actually paid by the assessee on or before the due date applicable in his case for furnishing the return of income under sub-section (1) of section 139
in respect of the previous year in which the liability to pay such sum was incurred as aforesaid and the evidence of such payment is furnished by the assessee
Therefore, any sum paid as bonus before filing of IT Return u/s 139(1) shall be allowed as expense for 2008-09.