Rashi on Deuteronomy 5:4/רש"י על דברים ה׳:ד׳

1 פנים בפנים FACE TO FACE — R. Berechia said: Thus did Moses, in effect, say: Do not think that I am misleading you with something which does not exist at all, as an agent does acting between the vendor and the purchaser; behold, the seller Himself is speaking to you (God who transmitted the Torah to you) (cf. Pesikta Rabbati 21: Pesachim Rabbah פ' י' הדברות קמייתא‎).