Мидраш к Бамидбар 5:21

2) You, too, do not wonder that even though one who tells his neighbor "Let us go and serve idolatry" is not liable, the hearer (if he does not testify to this) is liable. To this end, it is written "and he heard the voice of an alah," an alah being an oath, viz. (Bamidbar 5:21): "Then the Cohein shall beswear the woman with the oath of the alah." This tells me only of an oath accompanied by an alah (lit., a curse). Whence do I derive the same for an oath unaccompanied by an alah? From "and heard the alah" - "and heard the voice" ("of an oath"), equating an oath unaccompanied by an alah to an oath accompanied by an alah.

The law: If a Jewish person who passes before the ark [to lead the prayer], what is the law, should it be permitted for him to answer "Amen" after the [blessings of] the Kohanim? Such taught the sages: One who passes before the ark, he should not answer "Amen" after the Kohanim because of distraction. Our rabbis taught us: If he can answer without being distracted, he may answer. Why? Because nothing is greater before the Holy One, blessed be He, more than the "Amen" that the Jews answer. Rabbi Yehudah bar Simon: This "Amen" has three intentions. Oath, acceptance, faithfulness. How do we know "oath"? As its says, (Numbers 5:19-22) "The Kohen should put her under oath... and the woman is to say, Amen Amen."

… the prophets of Jerusalem were the first to sin, as it says “…for from the prophets of Jerusalem has falseness emanated to the whole land.” (Jeremiah 23:15) So too they were punished first and the rest did not escape, as it says “And a curse shall be taken from them…” (Jeremiah 29:22)

(Bamidbar 5:21) "Then the Cohein shall beswear the woman with the oath of the curse." What is the intent of this? Because it is written (Vayikra 5:1) "and he hear the voice of a curse," this tells me only of a curse. Whence do I derive that an oath is like a curse? It is derived inductively, viz.: It is written here (Bamidbar) "curse," and it is written elsewhere (Vayikra) "curse." Just as here "oath" is equated with "curse," (viz. "the oath of the curse"), so, there, "oath" is equated with "curse." And just as here, (the oath is administered) with "yod-keh" (viz. Ibid. "May the L-rd [yod-keh-vav-keh] render you, etc."), so, all the oaths in the Torah (are administered with) "yod-keh." "in the midst of your people": and your people (will remain at) peace. "in the midst of your people": and not at this time (when you are in the midst of gentiles.) There is a (crucial) difference between one being degraded in a place where he is known, and one being degraded in a place where he is not known, (the former degradation being more severe).