2 Peter 2:4-5

For if God did not spare angels when they sinned, but sent them to hell, putting them in chains of darkness to be held for judgment; if he did not spare the ancient world when he brought the flood on its ungodly people, but protected Noah, a preacher of righteousness, and seven others; ... 

For if God did not spare angels when they sinned 
Genesis 6:1-4  When human beings began to increase in number on the earth and daughters were born to them, the sons of God saw that the daughters of humans were beautiful, and they married any of them they chose. Then the LORD said, "My Spirit will not contend with humans forever, for they are mortal; their days will be a hundred and twenty years." The Nephilim were on the earth in those days--and also afterward--when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men and women.

putting them in chains of darkness to be held for judgment 
1 Timothy 3:6  He must not be a recent convert, or he may become conceited and fall under the same judgment as the devil.
Jude 6  And the angels who did not keep their positions of authority but abandoned their proper dwelling--these he has kept in darkness, bound with everlasting chains for judgment on the great Day.
Revelation 20:1-2  And I saw an angel coming down out of heaven, having the key to the Abyss and holding in his hand a great chain. He seized the dragon, that ancient serpent, who is the devil, or Satan, and bound him for a thousand years.

if he did not spare the ancient world 
2 Peter 3:6  By these waters also the world of that time was deluged and destroyed.

when he brought the flood on its ungodly people 
Genesis 7:23-24  Every living thing on the face of the earth was wiped out; people and animals and the creatures that move along the ground and the birds were wiped from the earth. Only Noah was left, and those with him on the ark. The waters flooded the earth for a hundred and fifty days. (see Genesis 6:5-8:19)

but protected Noah, a preacher of righteousness, and seven others 
Hebrews 11:7  By faith Noah, when warned about things not yet seen, in holy fear built an ark to save his family. By his faith he condemned the world and became heir of the righteousness that is in keeping with faith.
1 Peter 3:20  ... to those who were disobedient long ago when God waited patiently in the days of Noah while the ark was being built. In it only a few people, eight in all, were saved through water, ...

(parentheses are mine)

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