The command to follow the main body of Muslims (jama'ah)

It is narrated from Yusayr bin Amr (may Allah have mercy on him) that when Sayyiduna Uthman (may Allah be pleased with him) was martyred, Sayyiduna Abu Mas'ud al-Ansari (may Allah be pleased with him) set out towards Madinah. At that time I (Yusayr bin Amr) was suffering from a severe fever; despite that, I got my mount ready and caught up with him at a place called "al-Salihin". He was staying in a garden; when I went into the garden, I saw some people sitting in the far part of the garden. He had just performed ablution, and the water of the ablution was dripping from his blessed beard. I presented myself before him, praised and extolled Allah, the Mighty and Majestic, and then submitted: You had two trusted companions to whom people turned in any difficult matter, namely Sayyiduna Hudhayfah and Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with them both). I adjure you by Allah Almighty and I implore you by Islam: if you have heard anything from the Messenger of Allah (peace and blessings be upon him) about this fitnah, then do tell me; and if you have not heard anything, then give me your own reasoned judgement (ijtihad). He praised and extolled Allah Almighty and then said: "Hold fast to following the main body of the Ummah of Muhammad (peace and blessings be upon him), that is, the great majority (al-sawad al-a'zam), for Allah, the Mighty and Majestic, will never gather the Ummah of Muhammad (peace and blessings be upon him) upon misguidance. And remain patient until a righteous person finds rest (from the hardships of this world through death), or people find relief through the death of a wicked person."
It is also narrated from Yusayr bin Amr (may Allah have mercy on him) through another chain that when the martyrdom of Sayyiduna Ali (may Allah be pleased with him) took place, I met Abu Mas'ud (may Allah be pleased with him) at al-Salihin in the house of a landowner. I said to him: Tell me what you heard from the Messenger of Allah (peace and blessings be upon him), and do not hide it from me at all. He said: "O young man! We do not hide anything. Hold fast to the Jama'ah (the united body) and beware of division, for it is the very fitnah and utter misguidance. And surely Allah Almighty will never gather the Ummah of Muhammad (peace and blessings be upon him) upon misguidance."

It is narrated from Sayyiduna Jundub bin Sufyan (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Soon after me there will arise fitnahs like pieces of the dark night (in their horror); they will strike a person the way the foreheads of fighting bulls clash against each other. Such will be the severity of these fitnahs that a man will be a Muslim in the morning and will have become a disbeliever by evening, and he will be a believer in the evening and will reach the morning in a state of disbelief." A man said: O Messenger of Allah (peace and blessings be upon him)! What should we do in such a situation? He (peace and blessings be upon him) said: "Confine yourselves within the four walls of your houses, and efface your recognition and fame by choosing obscurity." The man asked again: O Messenger of Allah! What is your command if an attacker forcibly enters someone's house? He (peace and blessings be upon him) said: "Let him completely restrain his hand (from fighting in the fitnah), and let him accept being Allah's slain servant but never become Allah's killing servant; for at times a person, despite being under the canopy of Islam (claiming Islam), devours his brother's wealth, sheds his blood, disobeys his Lord and commits disbelief in his Creator, and Hell becomes obligatory for such a person."
Its chain is hasan (good).
Imam Abu Ya'la also narrated it from Muhammad bin Bakkar, from Abd al-Hamid bin Bahram, with the same wording.

It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The days and nights (that is, the span of this world) will not come to an end until one who stands up (a caller to fitnah) stands and cries out: Who will sell us his religion for a handful of dirhams?"
Abu Ya'la recorded it in his Musnad, and the theme of selling one's religion in the last age for a paltry worldly sum is established by authentic narrations in Sahih Muslim and other books of hadith.

It is narrated from Sayyiduna Ibn Umm Maktum (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) (once) came out at forenoon when the sun had risen high, and at that time some people were present near the apartments of the Mothers of the Believers. He (peace and blessings be upon him) said (addressing them): "O people of the apartments! The Fire (of Hell) has been kindled, and fitnahs have come like layers of the dark night (one after another). If you knew the realities that I know, you would surely weep much and laugh very little."
Imam Abu Bakr narrated it, and its narrators include Ishaq bin Sulayman al-Razi, Abu Sinan, Amr bin Murrah and Abu al-Bakhtari al-Ta'i.