Shevuos 3:6-7

Shevuos 3:6

If a person swore to refrain from a Torah obligation but he did not end up refraining, he is exempt. (His oath is ineffective because he is obligated to the contrary by the Torah.) If he swore to perform a mitzvah and he did not perform it, he is exempt. (His oath is ineffective because he is already obligated in the matter by the Torah.) One might think that he should be liable in this latter case, as follows: Rabbi Yehuda ben Beseira said that if one is liable for violating something that was not commanded at Sinai, all the more one should be liable for something that was commanded at Sinai! The Sages replied that such is not the case. If you say that one is liable for violating an oath in an optional matter, that’s because the Torah equated negative and positive oaths (in Leviticus 5:4, “to do bad or to do good”). This is not the case for an oath about a mitzvah, where the Torah does not equate negative (to refrain) with positive (to perform), since if someone swore to refrain from a mitzvah and then did not refrain, everyone agrees that he is exempt.

Shevuos 3:7

If a person said, “I swear I will not eat this loaf. I swear I will not eat it, I swear I will not eat it,” and then he ate it, he is only liable for one violation. This is a verbal oath for which one is liable to lashes if taken intentionally and to a korban olen v’yoreid (variable offering) if taken unintentionally. For an oath taken in vain, one is liable to lashes if it was taken intentionally and to a korban olen v’yoreid if it was taken unintentionally.