1 Enoch 6:2

1 And it came to pass when the children of men had multiplied that in those days were born unto them beautiful and comely daughters. 2 And the angels, the children of the heaven, saw and lusted after them, and said to one another: 'Come, let us choose us wives from among the children of men and beget us children.' 3 And Semjâzâ, who was their leader, said unto them: 'I fear ye will not indeed agree to do this deed, and I alone shall have to pay the penalty of a great sin.' 4 And they all answered him and said: 'Let us all swear an oath, and all bind ourselves by mutual imprecations not to abandon this plan but to do this thing.' 5 Then sware they all together and bound themselves by mutual imprecations upon it.

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

Lactantius Epitome of the Divine Institutes 27

But when God saw this, He sent His angels to instruct the race of men, and to protect them from all evil. He gave these a command to abstain from earthly things, lest, being polluted by any taint, they should be deprived of the honour of angels. But that wily accuser, while they tarried among men, allured these also to pleasures, so that they might defile themselves with women. Then, being condemned by the sentence of God, and cast forth on account of their sins, they lost both the name and substance of angels. Thus, having become ministers of the devil, that they might have a solace of their ruin, they betook themselves to the ruining of men, for whose protection they had come.

Date: 310-320 C.E.
* Dates are based on scholarly estimates