Reference for Nedarim 3:3

נִדְרֵי אֳנָסִים, הִדִּירוֹ חֲבֵרוֹ שֶׁיֹּאכַל אֶצְלוֹ, וְחָלָה הוּא אוֹ שֶׁחָלָה בְנוֹ אוֹ שֶׁעִכְּבוֹ נָהָר, הֲרֵי אֵלּוּ נִדְרֵי אֳנָסִין:

"Vows of constraint": If his friend bevowed him to eat with him, and he took ill, or his son took ill, or he were stopped by an (overflowing) river — these are vows of constraint. [For in the beginning it was not his intent that the vow "take" if he be detained perforce; and when the intent is evident, "the heart's thoughts" are entertained.]

Jastrow