Reference for Nedarim 3:1
אַרְבָּעָה נְדָרִים הִתִּירוּ חֲכָמִים, נִדְרֵי זֵרוּזִין, וְנִדְרֵי הֲבַאי, וְנִדְרֵי שְׁגָגוֹת, וְנִדְרֵי אֳנָסִים. נִדְרֵי זֵרוּזִין, כֵּיצַד. הָיָה מוֹכֵר חֵפֶץ וְאָמַר, קוֹנָם שֶׁאֵינִי פוֹחֵת לְךָ מִן הַסֶּלַע, וְהַלָּה אוֹמֵר, קוֹנָם שֶׁאֵינִי מוֹסִיף לְךָ עַל הַשֶּׁקֶל, שְׁנֵיהֶן רוֹצִין בִּשְׁלֹשָׁה דִינָרִין. רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב אוֹמֵר, אַף הָרוֹצֶה לְהַדִּיר אֶת חֲבֵרוֹ שֶׁיֹּאכַל אֶצְלוֹ, אוֹמֵר, כָּל נֶדֶר שֶׁאֲנִי עָתִיד לִדֹּר הוּא בָטֵל, וּבִלְבַד שֶׁיְּהֵא זָכוּר בִּשְׁעַת הַנֶּדֶר:
The sages permitted four vows (without absolution): the vows of the diligent, vows of exaggeration, vows of unwittingness, vows of constraint. "The vows of the diligent": How so? If one were selling something and said: "Konam if I sell it to you for less than a sela" [i.e., This loaf is konam to me if I sell it to you for less than a sela. A sela is four dinars], and the other said: "Konam, that I shall not give you more than a shekel" [a half-sela], both acquiesce in three dinars [and they did not intend a formal vow; but the seller "vowed" in order to "spur" the buyer to pay more, and the buyer, likewise, to get the seller to accept less, for which reason it is not a real vow. And even though "the heart's thoughts are of no account," here, where it is evident that this is their intent, this being the practice of buyers and sellers, we do entertain "the heart's thoughts."] R. Eliezer b. Yaakov says: Also one who wishes to bevow his friend to eat with him. [The gemara explains that something is lacking here and that this is what is meant: If one desires that his friend eat with him, and importunes him, and bevows him, this (too) is (in the category of) "the vows of the diligent." And if one wishes his vows of the entire year not to "take," he should arise on Rosh Hashanah and] say: "Let every vow that I shall make be void." [He need not necessarily do so on Rosh Hashanah, but the same obtains whenever he wishes to do so and for whichever time period he designates] so long as he is conscious [of the condition (that the vow not "take")] at the time of the vow, [and he wishes the condition to apply. Only then is the vow void. But if he were not conscious of the condition when he vowed or immediately thereafter, the vow "takes." And it goes without saying that if he were conscious of the condition when he vowed and desired that the condition be void and that the vow "take," it "takes." The laws of oaths and of vows are similar in this regard. The halachah is in accordance with R. Eliezer b. Yaakov.]