Proverbs 26:11
9 Like a thorn has gone up into the hand of a drunkard, so a proverb has gone up into the mouth of a fool. 10 Like an archer who wounds at random, so is the one who hires a fool or hires any passerby. 11 Like a dog that returns to its vomit, so a fool repeats his folly. 12 You have seen a man wise in his own opinion— there is more hope for a fool than for him. 13 The sluggard has said, “There is a lion in the road! A lion in the streets!”
2 Peter 2:22
20 For if after they have escaped the filthy things of the world through the rich knowledge of our Lord and Savior Jesus Christ, they again get entangled in them and succumb to them, their last state has become worse for them than their first. 21 For it would have been better for them never to have known the way of righteousness than, having known it, to turn back from the holy commandment that had been delivered to them. 22 They are illustrations of this true proverb: “A dog returns to its own vomit,” and “A sow, after washing herself, wallows in the mire.”
Notes and References
"... While in these two brief epistles there are several quotations of OT Scripture (2 Peter 2:22 with Proverbs 26:11; 3:8 with Psalm 90:4; 3:13 with Isaiah 65:17; Jude 9 with Zech 3:2) and possibly one of a Gospel text (2 Peter with Matthew 17:5), as well as one from an extracanonical writing (Jude 14–15 with 1 Enoch 1:9; 5:4; 60:8), the more distinctive feature of these writings is an appeal to Old Testament people or events that evoke episodes of divine salvation in the context of certain and devastating judgment and provide either moral or immoral example. While 2 Peter accentuates the certainty of God’s judgment upon perpetrators of destructive teaching and those who follow licentious ways (2 Peter 2), it also points to a moral example in two of the three citations: Noah saved from the devastating flood (Genesis 6–8) and Lot saved from the destruction of Sodom and Gomorrah (Genesis 19:12–29). Only in the first citation—God not sparing the rebellious angels (Genesis 6:1–6)— no saving act occurs ..."
Martin, Ralph P. Dictionary of the Later New Testament & Its Developments (p. 805) InterVarsity Press, 1997