Jubilees 4:15
14 At the end of the eighth jubilee [344-92] Kenan married his sister Mualelit. She gave birth to a son for him in the ninth jubilee, in the first week — in the third year of this week [395] — and he named him Malalael. 15 During the second week of the tenth jubilee [449-55] Malalael married Dinah, the daughter of Barakiel, the daughter of his father's brother. She gave birth to a son for him in the third week, in its sixth year [461]. He named him Jared because during his lifetime the angels of the Lord who were called Watchers descended to earth to teach mankind and to do what is just and upright upon the earth. 16 In the eleventh jubilee [491-539] Jared took a wife for himself, and her name was Barakah, the daughter of Rasu'eyal, the daughter of his father's brother, in the fourth week of this jubilee [512-18]. She gave birth to a son for him during the fifth week, in the fourth year of the jubilee [522], and he named him Enoch.
Pseudo Clementine Homilies 8.12
Clementine literatureFor of the spirits who inhabit the heaven, the angels who dwell in the lowest region, being grieved at the ingratitude of men to God, asked that they might come into the life of men, that, really becoming men, by more intercourse they might convict those who had acted ungratefully towards Him, and might subject every one to adequate punishment. When, therefore, their petition was granted, they metamorphosed themselves into every nature; for, being of a more godlike substance, they are able easily to assume any form. So they became precious stones, and goodly pearl, and the most beauteous purple, and choice gold, and all matter that is held in most esteem. And they fell into the hands of some, and into the bosoms of others, and suffered themselves to be stolen by them. They also changed themselves into beasts and reptiles, and fishes and birds, and into whatsoever they pleased. These things also the poets among yourselves, by reason of fearlessness, sing, as they befell, attributing to one the many and diverse doings of all.
Notes and References
"... Of these passages, drawn from a variety of sources, five attest the idea that the sexual sin of the angels was a result of their descent and not its purpose. Jubilees 4:15, Justin’s Apology, and it would seem Pseudo-Clementine Homilies indicate that the descent was for the purpose of instruction. Genesis 6:2 and Testament of Reuben 5 suggest that the women seduced the angels by means that 1 Enoch 8:2 attributes to angelic instruction. Taken together, this evidence indicates that the long reading of 1 Enoch 8:1 is not an accidental corruption but reflects very early tradition. Internal evidence corroborates this. Without the reference to the seduction of the watchers, the passage would have to imply a polemic against sexual seduction in general - a concern that is evident nowhere else in these chapters ..."
Nickelsburg, George W. E. A Commentary on the Book of 1 Enoch Chapters 1-36, 81-108 (p. 196) Fortress Press, 2001