It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The five prayers, the time from one Friday to the next, and from one Ramadan to the next, are an expiation for sins when the major sins are avoided."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20759