The instructions to the jury were in exact accordance with the well settled law. If the sum now sued for was allowed in the settlement between the parties, without fraud, by way of compromise of a doubtful claim, it could not be recovered back; but if it was paid by the plaintiffs, relying upon erroneous vouchers produced by the defendant at the time of the settlement, it might, even if there was no fraud, be recovered back as money paid by mistake. Riggs v. Hawley, 116 Mass. 596, 598. Merchants’ National Bank v. National Eagle Bank, 101 Mass. 281, 285. Paige v. Sherman, 6 Gray, 511. Union Bank v. Bank of United States, 3 Mass. 74. Exceptions overruled.