Shevuot 21A

קא משמע לן כדשני ליה.

it teaches us as Abaye answers him below.

ואיבעית אימא: כשם שמביא קרבן על שקר, כך מביא קרבן על שוא; ורבי עקיבא היא, דמחייב לשעבר כלהבא.

The Talmud offers an alternative resolution of the difficulty posed by the baraita: And if you wish, say that the assertion of the baraita that the prohibitions against taking an oath in vain and taking a false oath are one means: Just as one brings an offering for taking a false oath, so one brings an offering for taking an oath in vain. And this is in accordance with the opinion of R' Akiva, who deems one liable to bring an offering for taking an oath in vain that refers to the past, just as for taking a false oath that refers to the future.

מיתיבי: אי זו היא שבועת שוא ⁠– נשבע לשנות את הידוע לאדם. שבועת שקר ⁠– נשבע להחליף! אימא נשבע ומחליף.

The Talmud raises an objection to R' Yoḥanan’s distinction between a false oath and an oath taken in vain from a baraita: Which oath is an oath taken in vain? It is when one takes an oath to deny that which is known to people to be true. And a false oath is when one takes an oath that contradicts the past. The Talmud answers: Say, i.e., emend the baraita to say, that a false oath is when one takes an oath and subsequently contradicts it by acting otherwise.

כי אתא רבין, אמר רבי ירמיה, אמר רבי אבהו, אמר רבי יוחנן: ״אכלתי״ ו״לא אכלתי״⁠ – שקר, ואזהרתיה מ״לא תשבעו בשמי לשקר״. ״אוכל״ ו״לא אוכל״⁠ – עובר ב״לא יחל דברו״. ואי זו היא שבועת שוא? נשבע לשנות את הידוע לאדם.

§ When Ravin came from Eretz Yisrael to Babylonia, he reported that R' Yirmeya says that R' Abbahu says that R' Yoḥanan says: If one takes an oath, saying: I ate, or: I did not eat, it is a false oath if it is not true. And its prohibition in the Torah is from: “And you should not take an oath by My name falsely, so that you profane the name of your God; I am YHWH” (Leviticus 19:12). If one takes an oath, saying: I will eat, or: I will not eat, and breaks his oath, he violates the prohibition: “When a man vows a vow to YHWH, or takes an oath to bind his soul with a bond, he should not break his word” (Numbers 30:3). And which oath is an oath taken in vain? It is when one takes an oath to deny that which is known to people to be true.