Abu Ghalib narrates from Sayyiduna Abu Umamah (may Allah be pleased with him), from the Prophet (peace and blessings be upon him), regarding the saying of Allah, the Mighty and Majestic: "O you who believe, do not take as intimates those other than yourselves; they will spare no effort to harm you. They wish for your distress. Hatred has already appeared from their mouths, and what their breasts conceal is greater. We have made clear to you the signs, if you would use reason" [Al Imran: 118]. He said: "They are the Khawarij."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 8016