The declaration in Form 12B shall be furnished by a dealer before the refund sanctioning authority as referred to in sub-rule (2) of rule 76 or the appropriate auditing authority or the appropriate assessing authority, as the case may be, at any time on or before the date of hearing in connection with refund under clause (a), or clause (aa) or clause (ab), of section 61 or for audit under section 43 or assessment under section 46, by such authority:

Provided that if the appellate or revisional authority is satisfied that the dealer concerned was prevented by sufficient cause from furnishing such declaration within the time as aforesaid before the appropriate assessing authority or the refund sanctioning authority as referred to in sub-rule (2) of rule 76, as the case may be, such appellate or revisional authority may, for reasons to be recorded in writing, allow the dealer to furnish such declaration within the time fixed for hearing of appeal or revision, as the case may be.