It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Whoever dies having separated from the Jama'ah (the community) dies a death of Jahiliyyah (pre-Islamic ignorance)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13221