A NEGATIVE assurance opinion or statement is

A NEGATIVE assurance opinion or statement indicates that, based on the procedures performed and evidence obtained, the assurance provider did not identify any reasons to believe that the subject matter does not conform to the applicable criteria. This form of opinion does not provide absolute assurance but rather limited assurance, suggesting that nothing came to the auditor's attention that causes them to believe the subject matter is not fairly stated.References:

AICPA Auditing Standards

IIA Standards for the Professional Practice of Internal Auditing