Exodus 20:19

כה תאמר THUS THOU SHALT SAY — in this (the Holy) language (Mekhilta). אתם ראיתם YE HAVE SEEN — There is a difference between what a person himself sees and what others relate to him, for what others relate to him sometimes his heart is divided in its opinion so that he does not believe (Mekhilta). כי מן השמים דברתי THAT I HAVE SPOKEN [TO YOU] FROM HEAVEN — But another verse states, (Exodus 19:20) “And the Lord came down upon mount Sinai”, and thus the two verses appear to be contradictory! There now comes a third verse and harmonises them: (Deuteronomy 4:36) “Out of heaven He made thee hear His voice that He might instruct thee; and upon the earth He showed thee His great fire” — His glory was in the heavens but His fire and His power were upon the earth. Another explanation: He bent down the heavens and the heavens of heavens, and spread them out upon the mountain; similarly it states, (Psalms 18:10) “He bowed the heavens and came down” (Mekhilta) .

וַיֹּ֤אמֶר יְהֹוָה֙ אֶל־מֹשֶׁ֔ה כֹּ֥ה תֹאמַ֖ר אֶל־בְּנֵ֣י יִשְׂרָאֵ֑ל אַתֶּ֣ם רְאִיתֶ֔ם כִּ֚י מִן־הַשָּׁמַ֔יִם דִּבַּ֖רְתִּי עִמָּכֶֽם׃

And the Lord said to Moshe, Thus thou shalt say to the children of Yisra᾽el, You have seen that I have talked with you from heaven.