Translation:Shulchan Aruch/Choshen Mishpat/208

Paragraph 1- If a sale was performed illegally, such as where the parties raised the value of the item in exchange for delaying the payment of the money, or where they set a price before the market price emerged and the seller did not yet have the item or where he swore or vowed not to sell and he violated his oath and sold¸ and the sale was effected with a kinyan or another of the methods of transfer, the sale is valid and the buyer will pay the permissible rate. Neither party has the power to void the sale. The buyer can, however, retract from paying the higher rate. It makes no difference whether it is a case of sale, gift, waiver or anything else.