"When men began to increase on earth and daughters were born to them, the divine beings saw how beautiful the daughters of men were and took wives from among those that pleased them. The LORD said, 'My breath shall not abide in man forever, since he too is flesh; let the days allowed him be one hundred and twenty years.' It was then, and later too, that the Nephilim appeared on earth - when the divine beings cohabited with the daughters of men, who bore them offspring. They were the heroes of old, the men of renown." - Genesis 6:1-4

"They took wives unto themselves, and everyone (respectively) chose one woman for himself, and they began to go unto them. And they taught them magical medicine, incantations, the cutting of roots, and taught them (about) plants. And the women became pregnant and gave birth to great giants whose heights were three hundred cubits. These (giants) consumed the produce of all the people until the people detested feeding them. So the giants turned against (the people) in order to eat them." - 1 Enoch 7:1-5

"For it was on account of these three things [fornication, uncleanness, and injustice - see Jubilees 7:20] that the flood was on the earth, since (it was) due to fornication that the Watchers had illicit intercourse - apart from the mandate of their authority - with women. When they married of them whomever they chose they committed the first (acts) of uncleanness. They fathered (as their) sons the Nephilim. - Jubilees 7:21-22