Sayyiduna Arfajah (may Allah be pleased with him) said: The Prophet (peace and blessings be upon him) said: "Soon there will be trials and troubles" - he (peace and blessings be upon him) would draw out this word as he said it - "so whoever you see intending to divide the affair of my Ummah while it is united, kill him, whoever he may be."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14436