ישעיהו סד:ב פירוש: רש״י ואבן עזרא

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.

בעשותך When thou didst.

You descended to Mount Sinai, then mountains dripped from before You. In this manner, Dunash son of Labrat explained it.