וַיֹּאמֶר אֱלֹהִים יְהִי רָקִיעַ בְּתוֹךְ הַמָּיִם

וִיהִי מַבְדִּיל בֵּין מַיִם לָמָיִם.

وَقَالَ اللهُ: «لِيَكُنْ جَلَدٌ فِي وَسَطِ الْمِيَاهِ.

وَلْيَكُنْ فَاصِلاً بَيْنَ مِيَاهٍ وَمِيَاهٍ».

Y dijo Dios: Haya expansión en medio de las aguas,

y separe las aguas de las aguas.

And God said, Let there be a firmament in the midst of the waters,

and let it divide the waters from the waters.

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Additional LDS scriptural sources:

Moses 2:6
And again, I, God, said: Let there be a firmament in the midst of the water, and it was so, even as I spake; and I said: Let it divide the waters from the waters; and it was done;

Abraham 4:6
And the Gods also said: Let there be an expanse in the midst of the waters, and it shall divide the waters from the waters.

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Notes/Other Sources:Wikipedia entry for “firmament”

Google define function for “firmament”