It is reported from Sayyiduna Muhammad bin Surayh al-Ashja'i (may Allah be pleased with him) that he said: "Shall I not narrate to you a hadith which my ears heard and which my heart preserved, having heard it from the Prophet (peace and blessings be upon him)? Had I not heard this hadith from the Prophet (peace and blessings be upon him) once, or twice, or three times, or four times, or five times, or six times, or seven times, my estimation is that I would not have narrated it." The Prophet (peace and blessings be upon him) said: "When you are united as one community, and then someone comes who wants to create division within your community and split your staff, kill him, whoever among you he may be."
Al-Tabarani recorded it in al-Mu'jam al-Awsat. Its chain contains the narrator al-Abbas bin Awsajah, whom I do not know.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب قتال أهل البغي / 10434