Genesis 6:4-6

The Nephilim were in the earth in those days, and also after that, when the sons of God came in unto the daughters of men, and they bare children to them: the same were the mighty men which were of old, the men of renown. And the LORD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually. And it repented the LORD that he had made man on the earth, and it grieved him at his heart.