בַּעֲשׂוֹתְךָ֥ נוֹרָא֖וֹת לֹ֣א נְקַוֶּ֑ה יָרַ֕דְתָּ מִפָּנֶ֖יךָ הָרִ֥ים נָזֹֽלּוּ׃
你行了我們未曾盼望的可畏之事；你降臨了，眾山在你面前融化流淌。
Rashi
When You performed against the Egyptians and against all the adversaries awesome deeds, that we did not hope You would perform all those awesome deeds, for we were unworthy of them.
Rashi
You descended to Mount Sinai, then mountains dripped from before You. In this manner, Dunash son of Labrat explained it.