Tosefta sur Berakhot 4:3

Any [holiday] on which there is no Mussaf [prayer] for example, Chanukah and Purim, on Shacharit and Mincha he prays [the Shmoneh Esreh with] eighteen [Berachot (blessings)] and he says [the paragraph] about the occasion in [the Beracha of] Hodaah (Thanks). And if he did not say [the paragraph] about the occasion, he does not have to go back [to the beginning of Shmoneh Esreh]. And any [holiday] which has on it [the] Mussaf [prayer], for example Rosh Chodesh (New Month), and Chol Hamoed (the intermediate days of Sukkot and Pesach), on Shacharit and Mincha10 he would pray [the prayer of Shmoneh Esreh with] eighteen [Berachot] and he says [the paragraph] about the holiness of the day11 in [the Beracha of] Avodah (Temple Service).12 Rebbi Eliezer says, “[he says the paragraph about the holiness of the day] in [the Beracha of] Hodaah, and if he did not say it then he has to go back [to the beginning of Shmoneh Esreh].” In [the] Mussaf [prayer] he prays [the Shmoneh Esreh consisting of] seven [Berachot] and he says [the paragraph about the] holiness of the day in the middle [Beracha]. [On] Shabbat that fell out on Rosh Chodesh or on Chol Hamoed, during Shacharit and during Mincha he prays [the Shmoneh Esreh prayer that consists of] seven [Berachot] and he says [the paragraph about the] occasion in [the Beracha of] Avodah. Rebbi Eliezer says, “[He says the paragraph about the holiness of the day] in [the Beracha of] Hodaah, and if he did not say it then he has to go back [to the beginning of Shmoneh Esreh].” In [the] Mussaf [prayer] he prays [the Shmoneh Esreh consisting of] seven [Berachot] and he says [the paragraph about the] holiness of the day in the middle [Beracha]. On Shabbat, on Yom Tov (Pesach, Shavuot and Sukkot), and on Yom Kippur] he prays [the Shmoneh Esreh consisting of] seven [Berachot] and he says [the paragraph about the] holiness of the day in the middle [Beracha]. Rabban Shimon Ben Gamliel and Rebbi Yishmael the son of Rebbi Yochanan Ben Beroka say, “Any time that he is supposed to say seven [Berachot in Shmoneh Esreh] he says [the paragraph about the] holiness of the day in the middle [Beracha].”

[On] Yom Tov of Rosh Hashana which falls out to be on Shabbat, Bet Shamai say, “He prays ten [Berachot (blessings) in the Mussaf Shmoneh Esreh]. And he says [the Beracha] for Shabbat by itself and [the Beracha] for Yom Tov by itself, and he says [the Beracha] for Shabbat first.” And Bet Hillel say, “He prays nine [Berachot in the Mussaf Shmoneh Esreh].” [On any other] Yom Tov that falls out to be on Shabbat, Bet Shamai say, “He prays eight [Berachot in the Mussaf Shmoneh Esreh]. And he says [the Beracha] for Shabbat by itself and [the Beracha] for Yom Tov by itself, and he says [the Beracha] for Shabbat first.” And Bet Hillel say, “He prays seven [Berachot in the Mussaf Shmoneh Esreh]. He begins with [the Beracha about] Shabbat and ends with [the Beracha about] Shabbat and he says [the paragraph about] the holiness of the day in the middle [of the middle Beracha].” Rebbi Natan says, “He even seals [the middle Beracha with] Baruch [Ata Hashem] Mekadesh Hashabbat Veyisrael Vehazmanim (Blessed are You Hashem who sanctifies Shabbat, and Israel and the seasons).”

Eighteen Berachot (blessings) that the Sages have established [for the prayer of Shemoneh Esreh have been established] corresponding to eighteen mentionings [of God’s name] that are in [the chapter of Tehillim that begins with] “Ascribe to God, children of princes…” (Tehillim 29) And [a person] should include [the Beracha against] the heretics into [the Beracha] for the Rabbinical Jews, and [the Beracha] for the converts into [the Beracha] for the elders, and [the Beracha] for [King] David into [the Beracha] for [the rebuilding of] Jerusalem. But if he said each one of them separately he has fulfilled his obligation [of praying Shemoneh Esreh].