Book of Enoch Chapter 15: The origin of evil spirits
And He answered and said to me, and I heard His voice: 'Fear not, Enoch, thou righteous
man and scribe of righteousness: approach hither and hear my voice. And go, say to the Watchers of heaven, who have sent thee to intercede for them: "You should intercede" for men, and not men
for you: Wherefore have ye left the high, holy, and eternal heaven, and lain with women, and defiled yourselves with the daughters of men and taken to yourselves wives, and done like the children
of earth, and begotten giants (as your) sons? And though ye were holy, spiritual, living the eternal life, you have defiled yourselves with the blood of women, and have begotten (children) with the blood of flesh, and, as the children of men, have lusted after flesh and blood as those also do who die
and perish. Therefore have I given them wives also that they might impregnate them, and beget
children by them, that thus nothing might be wanting to them on earth. But you were formerly spiritual, living the eternal life, and immortal for all generations of the world. And therefore I have not appointed wives for you; for as for the spiritual ones of the heaven, in heaven is their dwelling.
And now, the giants, who are produced from the spirits and flesh, shall be called evil spirits upon
the earth, and on the earth shall be their dwelling. Evil spirits have proceeded from their bodies; because they are born from men and from the holy Watchers is their beginning and primal origin;
they shall be evil spirits on earth, and evil spirits shall they be called. [As for the spirits of heaven, in heaven shall be their dwelling, but as for the spirits of the earth which were born upon the earth, on the earth shall be their dwelling.]
And the spirits of the giants afflict, oppress, destroy, attack, do battle, and work destruction on the earth, and cause trouble: they take no food, but nevertheless
hunger and thirst, and cause offences. And these spirits shall rise up against the children of men and against the women, because they have proceeded from them.