The Second Epistle of Peter was also written by the apostle Peter in the middle of the first century. It warns of false teachers who had come into the Early Church and urges Christians to be brave and patient.

2 Peter 2

2:22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.