Genesis 6:2-4

that the sons of God saw the daughters of men, that they were beautiful; and they took wives for themselves of all whom they chose. And the LORD said, “My Spirit shall not strive with man forever, for he is indeed flesh; yet his days shall be one hundred and twenty years.” There were giants 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. Those were the mighty men who were of old, men of renown.