The Messenger of Allah ﷺ said, "Among the worst of people in the sight of Allah is the two-faced person."
حدثنا يحيى بن آدم حدثنا قطبة عن الأعمش عن أبي صالح
قال رسول الله ﷺ نجد من شر الناس عند الله ذا الوجهين
Its chain of transmission is sahih. Bukhari related it in the Book of Manners from Amr bin Hafs bin Ghiyath, Muslim related it in the Book of Manners from Yahya bin Yahya, Abu Dawud related it in the Book of Manners from Musaddad, Tirmidhi related it in the Book of Righteousness from Hannad bin Sari, and Imam Malik related it in Muwatta, in the Book of Jami, from Abu.