اَللَّهُمَّ اغْفِرْ لِي مَا قَدَّمْتُ وَمَا أَخَّرْتُ، وَمَا أَسْرَرْتُ وَمَا أَعْلَنْتُ
Transliteration
Allahummaghfir li ma qaddamtu wa ma akhkhartu, wa ma asrartu wa ma a'lantu
English meaning
O Allah, forgive me what I have done before and what I will do later, what I have done in secret and what I have done openly.
When is it recited?
In Ramadan and at all times.
Source
Muslim, Salat 222