Genesis 2:18-24:  The LORD God said, “It is not good that the man should be alone; I will make him a helper as his partner.” So out of the ground the LORD God formed every animal of the field and every bird of the air, and brought them to the man to see what he would call them; and whatever the man called every living creature, that was its name. The man gave names to all cattle, and to the birds of the air, and to every animal of the field; but for the man there was not found a helper as his partner. So the LORD God caused a deep sleep to fall upon the man, and he slept; then he took one of his ribs and closed up its place with flesh. And the rib that the LORD God had taken from the man he made into a woman and brought her to the man.

Then the man said, “This at last is bone of my bones and flesh of my flesh; this one shall be called Woman, for out of Man this one was taken.”

Therefore a man leaves his father and his mother and clings to his wife, and they become one flesh.