Sirach 16:7
Ben Sira, Ecclesiasticus5 Many such things my eye has seen, and my ear has heard things more striking than these. 6 In an assembly of sinners a fire is kindled, and in a disobedient nation wrath blazes up. 7 He did not forgive the ancient giants who revolted in their might. 8 He did not spare the neighbors of Lot, whom he loathed on account of their arrogance. 9 He showed no pity on the doomed nation, on those dispossessed because of their sins;
Baruch 3:26
24 O Israel, how great is the house of God, how vast the territory that he possesses! 25 It is great and has no bounds; it is high and immeasurable. 26 The giants were born there, who were famous of old, great in stature, expert in war. 27 God did not choose them, or give them the way to knowledge; 28 so they perished because they had no wisdom, they perished through their folly.
Notes and References
"... The interesting fact is that all these accounts of the myth of the Watchers are different from the biblical ones and, keeping in mind the modified aspects of the myth, especially those of the pseudo-Clementine version, they are close to the Enochic narrative. Biblical materials such as Genesis 6:1-8, Numbers 13:33, and Deuteronomy 1:28; 2:10, 21; 9:2 were most likely used in the Christian communities of the first centuries. While the text of Genesis 6 recounts the fornication of the sons of men (h’lhym) and mentions the presence of giants (nplym) on earth, the books of Numbers and Deuteronomy associate the giants with the terrestrial people of Anakites, the sons of Anak, the inhabitants of Hebron at the time when the Israelites came from Egypt; this association most likely reflects a different tradition. Several other fugitive references to the myth appear in Wisdom 14:6, Sirach 16:7, Baruch 3:26-8, Testament of Reuben 5:6, and Testament of Naphtali 3:5, and a larger remaking in Philo’s De Gigantibus 6-18 and 58-61 ..."
Giulea, Dragos-Andrei The Watchers' Whispers: Athenagoras's Legatio 25,1-3 and the Book of the Watchers (pp. 258-281) Vigiliae Christianae 61, 2007