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

Pirkei DeRabbi Eliezer 22:4

Rabbi Simeon said: From Seth arose and were descended all the generations of the righteous. From Cain arose and were descended all the generations of the wicked, who rebel and sin, who rebelled against their Rock, and they said: We do not need the drops of Thy rain, neither to walk in Thy ways, as it is said, "Yet they said unto God, Depart from us" (Job 21:14). Rabbi Meir said: || The generations of Cain went about stark naked, men and women, just like the beasts, and they defiled themselves with all kinds of immorality, a man with his mother or his daughter, or the wife of his brother, or the wife of his neighbour, in public and in the streets, with evil inclination which is in the thought of their heart, as it is said, "And the Lord saw that the wickedness of man was great in the earth" (Gen. 6:5). Rabbi said: The angels who fell from their holy place in heaven saw the daughters of the generations of Cain walking about naked, with their eyes painted like harlots, and they went astray after them, and took wives from amongst them, as it is said, "And the sons of Elohim saw the daughters of men that they were fair; and they took them wives of all that they chose" (Gen. 6:2). Rabbi Joshua said: The angels are flaming fire, as it is said, "His servants are a flaming fire" (Ps. 104:4), and fire came with the coition of flesh and blood, but did not burn the body; but when they fell from heaven, from their holy place, their strength and stature (became) like that of the sons of men, and their frame was (made of) clods of dust, as it is said, "My flesh is clothed with worms and clods of dust" (Job 7:5).

Date: 630-1030 C.E.
* Dates are based on scholarly estimates