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.' 5 Then they all took an oath together and bound themselves with a solemn promise to do so.
Tertullian Against Marcion 5.18
For He did not forbid (our first parents) a taste of the miserable tree, from any apprehension that they would become gods; His prohibition was meant to prevent their dying after the transgression. But the spiritual wickedness did not signify the Creator, because of the apostle's additional description, in heavenly places; for the apostle was quite aware that spiritual wickedness had been at work in heavenly places, when angels were entrapped into sin by the daughters of men. But how happened it that (the apostle) resorted to ambiguous descriptions, and I know not what obscure enigmas, for the purpose of disparaging the Creator, when he displayed to the Church such constancy and plainness of speech in making known the mystery of the gospel for which he was an ambassador in bonds, owing to his liberty in preaching — and actually requested (the Ephesians) to pray to God that this open-mouthed utterance might be continued to him?
Notes and References
"... The Latin church father Tertullian associates 1 Corinthians 11:10 with the tradition of the fall of the Watchers from Genesis 6. The veil was to designate them as married women and therefore unavailable, for the unveiled heads of virgins he considered particularly enticing to the angels. (There are similar references in Corona 14:2; Against Marcion 5.8.2; and On Prayer 22.5-6) ..."
Lewis, Scott M. "'Because of the Angels': Paul and the Enochic Traditions" in Harkins, Angela Kim, et al. (eds.) The Watchers in Jewish and Christian Traditions (pp. 81-90) Fortress Press, 2014