Pesachim 77A

שעירי ראשי חדשים איצטריכא ליה, סלקא דעתך אמינא הא לא כתיב בהו ״מועד״, קא משמע לן דראש חדש איקרי מועד,

It was necessary for the Mishnah to mention the goats sacrificed on the New Moons. It could enter your mind to say that since the term appointed time is not written with regard to them, these offerings do not override Shabbat or ritual impurity as do other communal offerings during their appointed times. Therefore, it teaches us that even Rosh Chodesh is called an appointed time.

כדאביי, דאמר אביי: תמוז דהאי שתא מלויי מליוה, דכתיב: ״קרא עלי מועד לשבר בחורי״.

This is in accordance with what Abaye said in order to defend the tradition that the spies returned from Eretz Yisrael and the entire Jewish people cried unnecessarily on the 9th of Av, which resulted in the 9th of Av becoming a day of crying for future generations. The calculation of the days does not work out precisely, and therefore Abaye said: They filled out Tammuz of that year, meaning that it was a 30-day month, rather than a 29-day month as it is nowadays. There is an allusion to this in a verse, as it is written: “He proclaimed an appointed time against me to crush my young men” (Lamentations 1:15), meaning that Rosh Chodesh was proclaimed in order to harm the Jewish people in the future. This proves that even Rosh Chodesh is called an appointed time.

למימרא דכולהו מ״מועד״ אתו, מנהני מילי? דתנו רבנן: ״וידבר משה את מעדי ה׳״⁠ — מה תלמוד לומר? לפי שלא למדנו אלא לתמיד ופסח שנאמר בהו ״במועדו״, ״במועדו״ ואפילו בשבת, ״במועדו״ ואפילו בטומאה.

The Talmud asks: Is that to say that all of them come from, i.e., are derived from, the term appointed time? From where are these matters derived? The Talmud answers: It is as A baraita states based upon the verse: “And Moses declared the appointed times of YHWH to the children of Israel” (Leviticus 23:44). What is the meaning when the verse states this phrase? This phrase is necessary because we had learned only that the daily offering and the Paschal lamb override Shabbat and ritual impurity, as it is stated with regard to them: In its appointed time, from which it is derived that each of them must be sacrificed in its appointed time and even on Shabbat, in its appointed time and even in ritual impurity.