1 Enoch 19:1

1 And Uriel said to me: 'Here shall stand the angels who have connected themselves with women, and their spirits assuming many different forms are defiling mankind and shall lead them astray into sacrificing to demons ⌈⌈as gods⌉⌉, (here shall they stand,) till ⌈⌈the day of⌉⌉ the great judgement in which they shall be judged till they are made an end of. 2 And the women also of the angels who went astray shall become sirens.'

Date: 200-50 B.C.E.
* Dates are based on scholarly estimates

Athenagoras Plea for the Christians 24

Embassy for the Christians

For this is the office of the angels — to exercise providence for God over the things created and ordered by Him; so that God may have the universal and general providence of the whole, while the particular parts are provided for by the angels appointed over them. Just as with men, who have freedom of choice as to both virtue and vice (for you would not either honour the good or punish the bad, unless vice and virtue were in their own power; and some are diligent in the matters entrusted to them by you, and others faithless), so is it among the angels. Some, free agents, you will observe, such as they were created by God, continued in those things for which God had made and over which He had ordained them; but some outraged both the constitution of their nature and the government entrusted to them: namely, this ruler of matter and its various forms, and others of those who were placed about this first firmament (you know that we say nothing without witnesses, but state the things which have been declared by the prophets); these fell into impure love of virgins, and were subjugated by the flesh, and he became negligent and wicked in the management of the things entrusted to him. Of these lovers of virgins, therefore, were begotten those who are called giants. And if something has been said by the poets, too, about the giants, be not surprised at this: worldly wisdom and divine differ as much from each other as truth and plausibility: the one is of heaven and the other of earth; and indeed, according to the prince of matter, We know we oft speak lies that look like truths.

Date: 175-180 C.E.
* Dates are based on scholarly estimates