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 And he was moreover with the angels of God these six jubilees of years, and they showed him everything which is on earth and in the heavens, the rule of the sun, and he wrote down everything. 22 And he testified to the Watchers, who had sinned with the daughters of men; for these had begun to unite themselves, so as to be defiled, with the daughters of men, and Enoch testified against (them) all. 23 And he was taken from amongst the children of men, and we conducted him into the Garden of Eden in majesty and honour, and behold there he writes down the condemnation and judgment of the world, and all the wickedness of the children of men. 24 And on account of it (God) brought the waters of the flood upon all the land of Eden; for there he was set as a sign and that he should testify against all the children of men, that he should recount all the deeds of the generations until the day of condemnation.
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