Genesis 6:1-4

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 fair and took as wives any they chose. The LORD said, “My Spirit will not always strive with man, for he is flesh; yet his days will be one hundred and twenty years.” The Nephilim were on the earth in those days, and also after that, when the sons of God came in to the daughters of men, and they bore children to them. These were the mighty men who were of old, men of renown.