Ṣaḥīḥ reporting in supplication and praising Allah the almighty

«اللهُمَّ اغْفِرْ لِي ذَنْبِي كُلَّهُ دِقَّهُ، وَجِلَّهُ، وَأَوَّلَهُ وَآخِرَهُ وَعَلَانِيَتَهُ وَسِرَّهُ»
{وهو دعاء يُشرع قوله في السجود}

allahumma ghfir li dhanbi kullahu diqqah, wa jillah, wa awwalahu wa akhirah, wa ʾalaniyatahu wa sirrah

O Allah, forgive me all my sins, great and small, the first and the last, those that are apparent and those that are hidden.

It is a supplication which to be said in prostration