Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "The five prayers, and from one Friday to the next, are an expiation for the sins in between, as long as he does not commit major sins (that is, as long as major sins do not overwhelm him)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4449