Section 12(10)(a) in The Central Sales Tax (Registration and Turnover) Rules, 1957
(a)A dealer may in support of his claim that he is not liable to pay tax under this Act in respect of any sale of goods on the ground that the sale of such goods is a sale in the course of export of these goods out of the territory of India within the meaning of sub-section (3) of Section 5, furnish to the prescribed authority a certificate in Form 'H' duly filled and signed by the exporter alongwith the evidence of export of such goods.