Related for Berakhot 125:4
כל כך למה לפי שאין עונין אמן במקדש ומנין שאין עונין אמן במקדש שנאמר (נחמיה ט, ה) קומו ברכו את ה' אלהיכם מן העולם עד העולם ואומר (נחמיה ט, ה) ויברכו (את) שם כבודך ומרומם על כל ברכה ותהלה
"Why all this? Because the response "Amen" was never made in the Sanctuary. Whence is it that "Amen" was never used as a response in the Sanctuary? As it is said, "Stand up and bless the Lord your God from everlasting to everlasting" (Nehem. ix. 5), and it continues, "And let them say: Blessed be Thy glorious Name, that is exalted above all blessing and praise" (ibid).
Tosefta Berakhot
The Beracha (blessing) of Zimun is from the Torah (i.e. a Torah obligation) as it is said, “And you should eat, and be satisfied, and bless…” (Deuteronomy 8:10), this is [a reference to] the Beracha of Zimun. “… Hashem, your God …” (Deuteronomy 8:10), this is [a reference to] the first Beracha [of Birkat Hamazon (Grace After Meals)]. “… for the land …” (Deuteronomy 8:10), this is [a reference to] the Beracha about the land (i.e. the second Beracha) [of Birkat Hamazon]. “… the good …” (Deuteronomy 8:10), this is [a reference to the Beracha about] Jerusalem (i.e. the third Beracha) [of Birkat Hamazon] as it is said “… this good mountain and Levanon.” (Deuteronomy 3:25). “… which He has given you.” (Deuteronomy 8:10), this is [a reference to the Beracha of] Hatov Vehameitiv (The Good and Who does good) (i.e. the fourth Beracha) [of Birkat Hamazon].
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