25 C.F.R. § 152.35
When the Indian owner and purchaser desire, a sale may be made or approved on the deferred payment plan. The terms of the sale will be incorporated in a memorandum of sale which shall constitute a contract for delivery of title upon payment in full of the amount of the agreed consideration. The deed executed by the grantor or grantors will be held by the Superintendent and will be delivered only upon full compliance with the terms of sale. If conveyance of title is to be made by fee patent, request therefor will be made only upon full compliance with the terms of the sale. The terms of the sale shall require that the purchaser pay not less than 10 percent of the purchase price in advance as required by the Act of June 25, 1910 (36 Stat. 855), as amended ( 25 U.S.C. 372 ); terms for the payment of the remaining installments plus interest shall be those acceptable to the Secretary and the Indian owner. If the purchaser on any deferred payment plan makes default in the first or subsequent payments, all payments, including interest, previously made will be forfeited to the Indian owner.
25 C.F.R. § 152.35