Josephus Antiquities of the Jews 1.3.1
1 Now this posterity of Seth continued to esteem God as the Lord of the universe, and to have an entire regard to virtue, for seven generations: but in process of time they were perverted, and forsook the practices of their fore-fathers; and did neither pay those honours to God which were appointed them, nor had they any concern to do justice towards men. But for what degree of zeal they had formerly shewn for virtue, they now shewed by their actions a double degree of wickedness. Whereby they made God to be their enemy. For many Angels of God accompanied with women, and begat sons that proved unjust, and despisers of all that was good; on account of the confidence they had in their own strength. For the tradition is, that these men did what resembled the acts of those whom the Grecians call Giants. But Noah was very uneasy at what they did: and being displeased at their conduct, persuaded them to change their dispositions, and their actions for the better. But seeing they did not yield to him, but were slaves to their wicked pleasures, he was afraid they would kill him, together with his wife and children, and those they had married. So he departed out of that land.
2 Peter 2:5
4 For if God did not spare the angels who sinned, but threw them into Tartarus16 and locked them up in chains in utter darkness, to be kept until the judgment, 5 and if he did not spare the ancient world, but did protect Noah, a herald of righteousness, along with seven others, when God brought a flood on an ungodly world, 6 and if he turned to ashes the cities of Sodom and Gomorrah when he condemned them to destruction, having appointed them to serve as an example to future generations of the ungodly, 7 and if he rescued Lot, a righteous man in anguish over the debauched lifestyle of lawless men, 8 (for while he lived among them day after day, that righteous man was tormented in his righteous soul by the lawless deeds he saw and heard)
Notes and References
"... 2 Peter 2:5 calls Noah, δικαιοσύνης κήρυκα, a herald of righteousness. There are no biblical texts that narrate Noah proclaiming righteousness to others; however, there are extra-biblical traditions that do. Sibylline Oracles 1.128–9 narrates God’s command to Noah, “Noah, embolden yourself, and proclaim repentance to all the peoples, so that all may be saved.” Here the proclamation of repentance results from the direct command of God. Sib. Or. 1.149–70, 173–198 contain the message of repentance that Noah preached. In other texts, Noah proclaims repentance, but there is no indication that he does so at the command of God. In Ant. 1.74, Josephus writes, “But Noah was very uneasy at what they did; and, being displeased at their conduct, persuaded them to change their dispositions and their acts for the better; but seeing they did not yield to him, but were slaves to their wicked pleasures, he was afraid they would kill him, together with his wife and children, and those they had married; so he departed out of that land.” Josephus does not use κῆρυξ or κηρύσσω here to speak of Noah’s actions. Rather, this text is another example of the tradition regarding the time that God gave for repentance before the flood arrived. In b. Sanhedrin 108a, Noah urges, “‘Repent; for if not, the Holy One, blessed be He, will bring a deluge upon you and cause your bodies to float upon the water like gourds.’” ..."
Devivo, Jenny 2 Peter 2:4-16: The Redaction of the Biblical and Intertestamental References Dependent on Jude 5-11 and Their Overall Significance (p. 70) Loyola University Chicago, 2014