A dealer who has claim for deduction under clause (b) of sub-section (1) of section 16 from his turnover of sales in accordance with rule 30C for sale under sub-section (3) of section 5 of the Central Sales Tax Act, 1956 (74 of 1956), shall, within three months from the end of the concerned return period to which such sale relates, furnish before the appropriate assessing authority a declaration in Form 12A in respect of such sale as obtained from the purchasing registered dealer:

Provided that if such appropriate assessing authority, upon application by the dealer, is satisfied that the dealer has been prevented by sufficient cause from furnishing such declaration within the time as stated, such appropriate assessing authority may allow the dealer further time, not beyond the date of hearing for audit under section 43 or for assessment under section 46, as he may deem fit, for furnishing such declaration.