42 C.F.R. § 433.140 : Public Health — CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF HEALTH AND HUMAN SERVICES — MEDICAL ASSISTANCE PROGRAMS — STATE FISCAL ADMINISTRATION — THIRD PARTY LIABILITY — FFP and repayment of Federal share

(a) FFP is not available in Medicaid payments if-
(1) The agency failed to fulfill the requirements of §§433.138 and 433.139 with regard to establishing liability and seeking reimbursement from a third party;
(2) The agency received reimbursement from a liable third party; or
(3) A private insurer would have been obligated to pay for the service except that its insurance contract limits or excludes payments if the individual is eligible for Medicaid.
(b) FFP is available at the 50 percent rate for the agency's expenditures in carrying out the requirements of this subpart.
(c) If the State receives FFP in Medicaid payments for which it receives third party reimbursement, the State must pay the Federal government a portion of the reimbursement determined in accordance with the FMAP for the State. This payment may be reduced by the total amount needed to meet the incentive payment in §433.153.

42 C.F.R. §433.140