اَللَّهُمَّ غْفِرْ لِي مَا قَدَّمْتُ وَمَا أَخَّرْتُ وَمَا أَسْرَرْتُ وَمَا أَعْلَنْتُ وَمَا أَسْرَفْتُ وَمَا أَنْتَ أَعْلَمُ بِهِ مِنِّي أَنْتَ الْمُقَدِّمُ، وَأَنْتَ الْمُؤَخِّرُ لَا إِلَهَ إِلَّا أَنْتَ

Allahum-maghfir lee maa qaddamtu, wa maa 'akhkhartu, wa maa 'asrartu, wa maa 'a'lantu, wa maa 'asraftu, wa maa 'Anta 'a'lamu bihi minnee. 'Antal-Muqaddimu, wa 'Antal-Mu'akhkhiru laa 'ilaaha 'illaa 'Anta

O Allah, forgive me what I have sent before me and what I have left behind me, what I have done in secret and what I have done in public, what I have done in excess, and those sins which You are better aware of than I. You are the One Who sends forth and You are the One Who delays. There is none worthy of worship but You. The Messenger of Allah (ﷺ) after the tashahood but before the salaam [1] and in another narration, it says he used to say this dua after finishing the prayer [2]. Both narrations are authentic. Perhaps he (ﷺ) sometimes said this dua before salaam and sometimes after salaam.

Reference: [1] Muslim: 771 [2] Sahih (Albani). Abu Dawud: 1509