Genesis 6:1-4

When humanity began to multiply on the surface of the earth, and daughters were born to them, the sons of God saw that the daughters of men were beautiful, and they took any that they wanted for themselves as wives. YHWH said, “My Spirit will not strive with humans forever, because they are flesh; so their days will be one hundred twenty years.” The Nephilim were in the earth in those days, and also after that, when the sons of God came in to the daughters of men and had children with them. Those were the mighty men who were of old, men of renown.