Epistle of Jude
He warns of "people who change the message about the grace of God in order to excuse their immoral ways" (verse 4).  He says this is not the faith "once delivered to the saints". He warns that we have stories in the bible of people who turned from trusting God to evil.  He lists the fallen angels, those saved from slavery in Eqypt and the people of Sodom and Gomorrah.  He also mentions individuals such as Cain who killed his brother, Balaam, and Korah.