Arfajah (may Allah be pleased with him) says: I heard the Prophet (peace and blessings be upon him) saying: "Soon there will be troubles upon troubles. So whoever wants to divide the affair of this Ummah while it is united, strike his head with the sword, whoever he may be."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16689