It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) would recite in his prostrations: 'Allahummaghfir li dhanbi kullahu, diqqahu wa jillahu, wa awwalahu wa akhirahu' (O Allah, forgive me all my sins, the small and the great, the first and the last; forgive them all). In the narration of Ibn al-Sarh there is the addition 'alaniyatahu wa sirrahu', meaning: "and forgive the open sins and the hidden ones too."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2687