Mishnayos Shevuos Perek 3 Mishnah 9

אכלה עבר על שבועת שוא – this is what he said: if he ate it , he has violated a oath taken in vain alone. If he didn’t eat it, he violated even an oath on a statement/rash oath (i.e., an oath taken by a person to reinforce a promise or an obligation or to confirm the veracity of a story – and is liable to bring a sing-offering). For once he swore that he would eat this loaf, he is obligated to eat it, and when he then took another oath [afterwards] that he would not eat it, he swore to abrogate/nullify the Mitzvah, and is flogged eause of the oath taken in vain, whether he would eat it or whether he would eat it, and if he did not eat it, he would be liable for two [violations], because of an oath taken in vain and because of oath on a statement/rash oath.