Rashi on Exodus 19:8/רש"י על שמות י״ט:ח׳

1וישב משה את דברי העם וגו׳ AND MOSES RETURNED THE WORDS OF THE PEOPLE [UNTO THE LORD] on the next day, which was the third of the month, for he never ascended the mountain to God except early in the morning (Shabbat 86a). But was it really necessary for Moses to deliver the reply to God; God is Omniscient! — But the explanation is that Scripture intends to teach you good manners from the example of Moses: for he did not say, “Since He who sent me knows the reply there is no need for me to report it” (Mekhilta).