The Consensus of the Community is a Valid Religious Authority
Two things have been identified as a great crime and as a cause of one's consignment to Hell in Verse An-Nisa 4:115 ⧉ وَمَن يُشَاقِقِ الرَّسُولَ مِن بَعْدِ مَا تَبَيَّنَ لَهُ الْهُدَىٰ (And whoever breaks away with the Messenger after the right path has become clear to him...). The first is opposing the Messenger of Allah. Obviously, doing so is Kufr (disbelief, infidelity) and a terrible curse. The second crime relates to a violation of universal Muslim consensus. It means the abandoning of something which has the universal agreement of all Muslims and opting for some other way against them. This explains that the consensus of the Muslim community has valid religious authority. In other words, we know that following the injunctions given in the Qur'an and Sunnah is obligatory. Similarly, when the Muslim Ummah (Community) agrees about something universally, following its consensus becomes equally obligatory. Any opposition to this consensus is a grave sin as was said by the Holy Prophet ﷺ in a hadith:
یَدُ اللہِ عَلَی الجمعۃِ مَن شَدَّ شُذَّ فِی النَّار
That is, the hand of Allah is on the Muslim community. Whoever breaks away or separates himself from it will himself be separated for consignment to Hell.
Imam al-Shafi` (رح) was asked: 'Can the validity of the authority of the Consensus of Muslim Ummah be proved from the Holy Qur'an?' He devoted to the recitation of the Qur'an full three days, completing three recitals each during the day and night. Finally, the proof that he came up with was this verse. When he cited it before scholars, they all agreed: This proof is sufficient to confirm the authority of ` Ijma`, the Consensus of Muslim Community