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."
Cross References (ranked by relevance)
He hath made the earth by his power, he hath established the world by his wisdom, and hath stretched out the heaven by his understanding.
Hast thou with him spread out the sky, which is strong, and as a molten looking glass?
By the word of the LORD were the heavens made; and all the host of them by the breath of his mouth.
Who coverest thyself with light as with a garment: who stretchest out the heavens like a curtain:
Praise him, ye heavens of heavens, and ye waters that be above the heavens.
For he spake, and it was done; he commanded, and it stood fast.
The heavens declare the glory of God; and the firmament sheweth his handywork.
The burden of the word of the LORD for Israel, saith the LORD, which stretcheth forth the heavens, and layeth the foundation of the earth, and formeth the spirit of man within him.
And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven.
Praise ye the LORD. Praise God in his sanctuary: praise him in the firmament of his power.
By his spirit he hath garnished the heavens; his hand hath formed the crooked serpent.
Also by watering he wearieth the thick cloud: he scattereth his bright cloud:
If the clouds be full of rain, they empty themselves upon the earth: and if the tree fall toward the south, or toward the north, in the place where the tree falleth, there it shall be.
And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: