Cross reference
Genesis 7:17
17 And for forty days the waters were over all the earth; and the waters were increased so that the ark was lifted up high over the earth.
Genesis 7:4
4 For after seven days I will send rain on the earth for forty days and forty nights, for the destruction of every living thing which I have made on the face of the earth.
Genesis 7:12
12 And rain came down on the earth for forty days and forty nights.