25 C.F.R. § 1000.401
This section applies to BIA programs, services, functions, or activities, notwithstanding any other provision of law. Any funds appropriated under the Snyder Act of 1921 (42 Stat. 208), for any fiscal year that are not obligated or spent by the end of the fiscal year for which they were appropriated shall remain available for obligation or expenditure during the following fiscal year. In the case of amounts made available to a Tribe/Consortium under an AFA, if the funds are to be expended in the succeeding fiscal year for the purpose for which they were originally appropriated, contracted or granted, or for which they are authorized to be used under the provisions of § 106(a)(3) of the Act, no additional justification or documentation of such purposes need be provided by the Tribe/Consortium to the Secretary as a condition of receiving or expending such funds.
25 C.F.R. § 1000.401