Midrash su Esodo 39:3

"And God said 'let there be a firmament in the midst of the waters'". The rabbis said regarding this in the name of Rabbi Chanina, but Rabbi Pinchas and Rabbi Jacob the son of Rabbi Avin said this in the name of Rabbi Samuel son of Nachman: "when the Holy One, blessed be He, said 'let there be a firmament in the midst of the waters', the middle liquid layer solidified, and the lower heavens were formed, and the heavens above the heavens, the upper ones [were formed]". Rab said "their works on the first day were liquid and on the second they were solid. "Let there be a firmament" [means] let the firmament solidify". Rabbi Yehudah the son of Rabbi Simon said "['let there be a firmament' means] let a thin plating be made for the firmament (raqi'a), just as you see it said "and they beat thin (vayeraq'u) the plates of gold (Exodus 39:3)"". Rabbi Chanina said "the fire came forth from above and dried the surface of the firmament [solidifying it]". Rabbi Yochanan came to this conclusion with this verse: "By His breath [meaning fire] the heavens are smoothed (Job 26:13)." He used to say: "Rabbi Chanina taught me well". Rabbi Yudan the son of Rabbi Shimon said "the fire went forth from above and it made the surface of the firmament gleam". R. Berakhyah, R. Yaakov bar R. Avina in the name of R. Abbah bar Kahana said: The work of creation came to teach about the giving of the Torah, and the teaching was revealed through it: "As when fire kindles the parts” (Isaiah 64:1)—its halves. When did the fire split between the upper and lower [heavens], is it not when the Torah was given!? Thus it was at the creation of the universe.Thus it was at the creation of the universe."