Yusayr bin Amr (may Allah be pleased with him) said: When Sayyiduna Ali (may Allah be pleased with him) was martyred, I saw Sayyiduna Abu Mas'ud (may Allah be pleased with him), so I followed him and said: "I ask you by Allah, what did you hear from the Prophet (peace and blessings be upon him) about the trials (fitan)?" He said: "We do not conceal anything. You must fear Allah and stay with the community (jama'ah), and beware of division, for it is misguidance itself; and Allah, the Mighty and Majestic, will not gather the Ummah of Muhammad (peace and blessings be upon him) upon misguidance."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14737