Genesis 1:6
"And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters."Genesis 1:6 (KJV)
Context from Genesis 1
4
And God saw the light, that it was good: and God divided the light from the darkness.
5
And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
6
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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And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
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And God called the firmament Heaven. And the evening and the morning were the second day.