Declaration requirement for firms: timely prescribed declaration ties to entitlement, with officer discretion for sufficient cause. The amendment requires a firm to furnish, before expiry of the time allowed for furnishing the return of income for the subsequent assessment year under section 139(1) or (2) (including extensions), a declaration in the prescribed form and verified in the prescribed manner; the Income-tax Officer may, if satisfied that the firm was prevented by sufficient cause, allow the declaration to be furnished after that time but only before the assessment is made.