Va. Code Ann. § 2.2-1822

The Comptroller shall not issue a disbursement warrant unless and until he has audited, through the use of statistical sampling or other acceptable auditing techniques the bill, invoice, account, payroll or other evidence of the claim, demand or charge and satisfied himself as to the regularity, legality and correctness of the expenditure or disbursement, and that the claim, demand or charge has not been previously paid. If he is so satisfied, he shall approve the same; otherwise, he shall withhold his approval. In order that such regularity and legality may appear, the Comptroller may, by general rule or special order, require the certification or other evidence as the circumstances may demand.