Genesis 6:1-4

When men began to multiply on the face of the ground, and daughters were born to them, the sons of God saw that the daughters of men were fair; and they took to wife such of them as they chose. Then the LORD said, “My spirit shall not abide in man for ever, for he is flesh, but his days shall be a hundred and twenty years.” The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of men, and they bore children to them. These were the mighty men that were of old, the men of renown.