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

Irenaeus Against Heresies 4.36

4 Since the Son of God is always one and the same, He gives to those who believe in Him a well of water [springing up] to eternal life, but He causes the unfruitful fig-tree immediately to dry up; and in the days of Noah He justly brought on the deluge for the purpose of extinguishing that most infamous race of men then existent, who could not bring forth fruit to God, since the angels that sinned had commingled with them, and [acted as He did] in order that He might put a check upon the sins of these men, but [that at the same time] He might preserve the archetype, the formation of Adam. And it was He who rained fire and brimstone from heaven, in the days of Lot, upon Sodom and Gomorrha, an example of the righteous judgment of God, that all may know, that every tree that brings not forth good fruit shall be cut down, and cast into the fire. And it is He who uses [the words], that it will be more tolerable for Sodom in the general judgment than for those who beheld His wonders, and did not believe in Him, nor receive His doctrine. For as He gave by His advent a greater privilege to those who believed on Him, and who do His will, so also did He point out that those who did not believe in Him should have a more severe punishment in the judgment; thus extending equal justice to all, and being to exact more from those to whom He gives the more; the more, however, not because He reveals the knowledge of another Father, as I have shown so fully and so repeatedly, but because He has, by means of His advent, poured upon the human race the greater gift of paternal grace.

Date: 175-190 C.E.
* Dates are based on scholarly estimates