Genesis 6:1-4

Now when men began to multiply on the face of the earth and daughters were born to them, the sons of God saw that the daughters of men were beautiful, and they took as wives whomever they chose. So the Lord said, “My Spirit will not contend with man forever, for he is mortal; his days shall be 120 years.” The Nephilim were on the earth in those days— and afterward as well— when the sons of God had relations with the daughters of men. And they bore them children who became the mighty men of old, men of renown.