Then 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
Surrounding context
1:5 God called the light Day, and the darkness He called Night. So the evening and the morning were the first day.
1:6 Then God said, "Let there be a firmament in the midst of the waters, and let it divide the waters from the waters."
1:7 Thus 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.