It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "An obligatory prayer until the next prayer, and Jumu'ah until the next Jumu'ah, and the month until the next month - that is, from Ramadan to Ramadan - are an expiation for the sins committed between them." The narrator says: Then after that he (peace and blessings be upon him) said: "Except for three things (which are not forgiven through them): associating partners with Allah, breaking the pledge, and abandoning the Sunnah. Breaking the pledge means that you give your pledge of allegiance to the imam, then turn against him and fight him with your sword; and abandoning the Sunnah means leaving the Jama'ah (the main body of Muslims)." This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.