[If] one swore to annul a mitzvah, and did not annul it —- he is exempt; to fulfill [a mitzvah], and he did not fulfill [it] —- he is exempt. For it might have been inferred that he be liable, as is the opinion of R' Yehudah ben Beseira. Said R' Yehudah ben Beseira: If for an optional matter, concerning which he was not adjured from Mount Sinai, he is liable; [then] for a mitzvah, concerning which he is adjured from Mount Sinai, is it not certain that he should be liable? They said to him: No! If you say this as regards an optional oath, it is because [Scripture] has made negative equal to positive in that regard. Will you say this in the case of an oath to fulfill a mitzvah, in which [Scripture] did not make negative equal to positive? For if he swears to annul it and does not annul it, he is exempt.

“I swear that I will not eat this loaf”; “I swear that I will not eat it”; “I swear that I will not eat it,” and he ate it —- he is liable only once. This is the oath of utterance for which one is liable for its willful transgression to [a penalty of] lashes, and for its inadvertent transgression to a variable [sin-] offering. [For] a vain oath —- one is liable for its willful transgression to [a penalty of] lashes, and for its inadvertent transgression, one is exempt.