And it is hereby enacted, that it shall be competent to the Collector at any time before the sale of an estate shall have commenced to exempt such estate form sale ; and in like manner it shall be competent to the Commissioner of Revenue at any time before the sale of an estate shall have commenced, to exempt such estate from sale, by a special order to the Collector to that effect in each case ; and no sale of an estate shall be legal if held after the receipt of an order of exemption in respect, to such estate. Provided, however, and it is hereby enacted, that the Collector or Commissioner shall duly record in a proceeding the reason for granting such exemption; and provided also, that an order for exemption so issued by the Commissioner shall not affect the legality of a sale which may have taken place before the receipt by the Collector of the order for exempting it from sale.