Genesis 6:2-4

2that the sons of 1God saw the daughters of men that they were fair, and took themselves wives of all that they chose.

3And Jehovah said, My Spirit shall not always plead with Man; for he indeed is flesh; but his days shall be a hundred and twenty years.

4In those days were the giants on the earth, and also afterwards, when the sons of 2God had come in to the daughters of men, and they had borne [children] to them; these were the heroes, who of old were men of renown.