اللَّهُمَّ اغْفِرْ لِي ذَنْبِي كُلَّهُ دِقَّهُ وَجِلَّهُ أَوَّلَهُ وَآخِرَهُ سِرَّهُ وَعَلانِيَتَهُ

‘Allaahumma ighfirlee Dhanbee kullah, diqqahu wa jillahu, awwalahu wa aakhirahu, sirrahu wa alaaniyatahu

O Allaah forgive all my sins, the minute of them and the major of them, the first of them and the last of them, the ones committed secretly and openly.

[Collected by Muslim]

Taken from the Fatawaa of our Shaykh, Allaama,

The Mufti of the Kingdom of Saudi Arabia, Abdul Azeez bin Abdullaah Bin Baz

Translated by Abbas Abu Yahya

https://followingthesunnah.wordpress.com/2015/06/30/the-best-dua-supplication