Genesis 7:12
And the rain was upon the earth forty days and forty nights.
Cross-reference
Genesis 7:4
Prophetic fulfillment
Genesis 7:4 predicts the forty days of rain that 7:12 records as happening — a direct fulfillment of God's warning.
Genesis 7:17
Parallel
Genesis 7:17 continues the narrative: the flood lasted forty days, building on the rain that began in 7:12.
Genesis 1:6
Contrast
In Genesis 1:6, God separates waters above from below — the flood rains here reverse that separation, collapsing the firmament's boundary.