1 Enoch 6:2
1 And it came to pass when the population of humans had increased during those times, beautiful and attractive daughters were born to them. 2 And the angels, the children of heaven, saw them and desired them, and said to each other: 'Come, let us choose wives from among the humans and father children.' 3 And Semjâzâ, their leader, said to them: 'I fear that you will not actually agree to do this, and I alone will have to pay the penalty of a great sin.' 4 And they all replied to him and said: 'Let us all take an oath, and all bind ourselves with a solemn promise not to abandon this plan but to carry out this act.'
Jubilees 4:22
21 He was, moreover, with God's angels for six jubilees of years. They showed him everything on earth and in the heavens — the dominion of the sun — and he wrote down everything. 22 He testified to the Watchers who had sinned with the daughters of men because these had begun to mix with earthly women so that they became defiled. Enoch testified against all of them. 23 He was taken from human society, and we led him into the Garden of Eden for his greatness and honor. Now he is there writing down the judgment and condemnation of the world and all the wickedness of mankind. 24 Because of him the flood water did not come on any of the land of Eden because he was placed there as a sign and to testify against all people in order to tell all the deeds of history until the day of judgment.
Notes and References
"... For Jubilees, in distinction from the traditions represented in 1 Enoch, the angels’ descent was a positive event—they came on a teaching mission and to model righteous behavior. Only at a later time — and upon the earth—did problems arise. So, the angels did not become sinful in their heavenly home prior to their descent (as they probably did according to 1 Enoch 6:2; 12:4; 15:3; 16:3); that happened only after they had left it. The reputation of heaven thus remains intact. Jubilees does not give an exact date for the descent of the angels (“during his [Jared’s] lifetime”), but Syncellus puts it in the year 1000, which was Jared’s fortieth year. Since his chronology is five hundred years higher than the one in Jubilees at this point, his date is otherwise just one year off the one in Jubilees for Jared’s fortieth year (461 + 40 = 501). The year 1000 seems highly significant in Syncellus’s chronology, while in Jubilees the event is in the tenth jubilee period—possibly a significant one ..."
VanderKam, James C., and Sidnie White Crawford Jubilees: A Commentary on the Book of Jubilees (p. 249) Fortress Press, 2018