It is narrated from Sayyiduna al-Harith al-Ash'ari (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said to us: "I command you with five things which Allah Almighty has commanded me: 'al-sam'' (listening), 'al-ta'ah' (obedience), 'al-jama'ah' (the community), 'al-hijrah' (emigration) and 'al-jihad fi sabilillah' (striving in the path of Allah). Whoever separates from the community by even a hand-span has removed the noose of Islam from his neck, unless he returns; and whoever makes a call of jahiliyyah is among the people of Hell." A man said: Even if he observes prayer and fasting? He (peace and blessings be upon him) said: "Even if he observes prayer and fasting. Call people with the call of Allah, Who has named you Muslims, believers and servants of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16613