Notwithstanding anything contained in Rule 46 or Rule 49 or Rule 54, where a registered person is supplying taxable as well as exempted goods or services or both to an unregistered person, a single "invoice-cum-bill of supply" may be issued for all such supplies.

'Provided that the said single "invoice-cum-bill of supply" shall contain the particulars as specified under rule 46 or rule 54, as the case may be, and rule 49.