Sayyiduna Abu Sa'id (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) said: "There will be a split between two groups of my Ummah, and a breakaway group will break away from between them; the one of the two groups closer to the truth will fight it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16695