42 C.F.R. § 417.481
A risk contract must provide that the HMO or CMP agrees to maintain and make available to CMS upon request, books, records, documents, and other evidence of acounting procedures and practices that—
(a) Are sufficient to—
[50 FR 1346, Jan. 10, 1985, as amended at 58 FR 38082, July 15, 1993; 60 FR 45680, Sept. 1, 1995]