וַיַּ֨עַן בְּנָיָ֧הוּ בֶן־יְהֽוֹיָדָ֛ע אֶת־הַמֶּ֖לֶךְ וַיֹּ֣אמֶר ׀ אָמֵ֑ן כֵּ֚ן יֹאמַ֣ר יְהוָ֔ה אֱלֹהֵ֖י אֲדֹנִ֥י הַמֶּֽלֶךְ׃
Da rief Benajahu, Sohn Jojadas, dem König zu und sprach: Amen! Also wolle der Gott meines Herrn, des Königs!
Mesillat Yesharim
Our sages of blessed memory roused us to the truth of this matter in reference to the coronation of Shlomo. David told Beniyahu (in Melachim 1:33-36) "take him down to Gihon". Beniyahu replied: "Amen, may G-d say so [too]".