מִי שֶׁנִּשְׁבַּע שֶׁלֹּא יֹאכַל הַיּוֹם כְּלוּם וְאָכַל פָּחוֹת מִכְּזַיִת פָּטוּר. שֶׁאֵין אֲכִילָה פְּחוּתָה מִכְּזַיִת. וַהֲרֵי הוּא כְּאוֹכֵל חֲצִי שִׁעוּר מִנְּבֵלוֹת וּטְרֵפוֹת וְכַיּוֹצֵא בָּהֶן. וְאִם אָמַר שְׁבוּעָה שֶׁלֹּא אֹכַל דָּבָר זֶה וַאֲכָלוֹ חַיָּב. וַאֲפִלּוּ הָיָה הַדָּבָר שֶׁנִּשְׁבַּע עָלָיו זֶרַע חַרְדָּל אֶחָד אוֹ פָּחוֹת מִמֶּנּוּ:
When a person takes an oath that he will not eat anything on that day and he ate less than an olive-sized portion of food, he is not liable. For "eating" does not involve a quantity less than an olive-sized portion. It is as if he partook of less than the minimum measure of a nevelah, a trefe, or the like. If he said: "[I am taking] an oath that I will not eat this substance," and he ate it, he is liable even if the substance concerning which he took the oath is one mustard seed or smaller.
