The Messenger of Allah ﷺ used to say while prostrating himself: O Lord, forgive me all my sins, small and great, first and last, open and secret.
أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يَقُولُ فِي سُجُودِهِ اللَّهُمَّ اغْفِرْ لِي ذَنْبِي كُلَّهُ دِقَّهُ وَجِلَّهُ وَأَوَّلَهُ وَآخِرَهُ وَعَلاَنِيَتَهُ وَسِرَّهُ