Nombres 30:3

A vow. By saying, ‘Let it be as a konam to me, that I will not eat, or I may not do a certain thing.’ But perhaps, even if he swears to eat the meat of an animal that was not ritually slaughtered, I read, concerning him, “all that he has verbalized, he must fulfill”? The Torah, therefore, teaches, “. . .to initiate a prohibition”— to prohibit what is permitted, but not to permit what is prohibited.

He may not profane his word. Like Gא יְחַלֵּל דְבָרוֹ, he may not secularize his word.

A man, a son of thirteen when he shall have vowed a vow before the Lord, or have sworn an oath, saying, I will withhold from such a thing which is permitted to me, shall not be allowed to relax his word (at his own will): nevertheless, the house of judgment (beth dina) can absolve him; but if they absolve him not, whatsoever hath gone out of his mouth he shall perform.

IF A MAN ‘YIDOR NEDER’ (VOWETH A VOW). “[This means if] a person says: ‘May there be konam is a substitute for korban (offering), and is used for a vow of abstinence, meaning, “May this object be forbidden to me in the same way as it is forbidden to have any benefit from a holy offering.” upon me that I shall not eat, or that I shall not do such-and-such a thing.’ I might think that even [if he vowed] that he would eat n’veilah is an animal that has died a natural death, or was not properly slaughtered. Treifah is an animal suffering from a certain serious organic disease, even if it is properly slaughtered. Both are forbidden to be eaten by law of the Torah. See Vol. III, p. 343, Note 96. [which is forbidden by the Torah to be eaten] I apply to him [the verse], he shall do according to all that proceedeth out of his mouth. Scripture therefore says, to bind his soul with a bond, which means [that he has the power] to forbid [upon himself] that which was [hitherto] permitted to him, but not to allow himself to do that which is forbidden [by means of vowing to do it].” This is Rashi’s language. But the text of the Sifre 153. is not so. Instead the Rabbis taught there [the following explanation] of [the expression] to bind his soul with a bond: “I might think that even if ‘he swore’ to eat n’veiloth and treifoth, is an animal that has died a natural death, or was not properly slaughtered. Treifah is an animal suffering from a certain serious organic disease, even if it is properly slaughtered. Both are forbidden to be eaten by law of the Torah. See Vol. III, p. 343, Note 96. abominable things and reptiles, I apply to him [the verse], he shall do according to all that proceedeth out of his mouth. Scripture therefore says, to bind his soul with a bond, which means [that he has the power] to forbid [upon himself] that which was [hitherto] permitted to him, but not to bind himself to do that which is forbidden [by means of vowing to do that which is prohibited by the Torah].” Thus the Rabbis [in the Sifre] mentioned this matter in connection with shevuoth (oaths), and the Rabbi [Rashi] changed it to apply to nedarim (vows).. Ramban’s intent is to point out that Rashi, who made his comment on the phrase if a man voweth a vow, and speaks of konam [a term used only in vows], is diverging from the Sifre who gives this …

ככל היוצא מפיו יעשה. This refers to the words השבע שבועה, meaning that the party concerned must do as he has sworn to do and in accordance with the date he had specified whether in the immediate future or at a later date. Proof that this is the correct interpretation of our verse is what Moses himself said in Deut. 23,22 כי תדור נדר לה' לא תאחר לשלמו “when you make a vow to the Lord your G’d, do not be tardy in paying it;” this is followed immediately by מוצא שפתיך תשמור ועשית, “the utterance that emanates from your mouth you shall honour, and carry out the respective undertaking.”