كتاب الأذكار
16
The Book of the Remembrance of Allah
'Ali (May Allah be pleased with him) reported:
When the Messenger of Allah (ﷺ) was in Salat (prayer), he used to supplicate towards the end of prayer after Tashahhud and before the concluding salutations: "Allahum-maghfir li ma qaddamtu wa ma akh-khartu, wa ma asrartu, wa ma a'lantu, wa ma asraftu, wa ma Anta a'lamu bihi minni. Antal-Muqqadimu, wa Antal-Mu'akh-khiru. La ilaha illa Anta (O Allah! Forgive my former and latter sins, which I have done secretly and those which I have done openly, and that I have wronged others, and those defaults of mine about which You have better knowledge than I have. You Alone can send whomever You will to Jannah, and You Alone can send whomever You will to Hell-fire. None has the right to be worshipped but You."

[Muslim].
وعن علي رضي الله عنه قال‏:‏ كان رسول الله صلى الله عليه وسلم إذا قام إلى الصلاة يكون من آخر ما يقول بين التشهد والتسليم‏:‏ ‏ "‏اللهم اغفر لي ما قدمت وما أخرت، وما أسررت وما أعلنت، وما أسرفت، وما أنت أعلم به مني، أنت المقدم، وأنت المؤخر، لا إله إلا أنت‏"‏ ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏
Sunnah.com reference : Book 16, Hadith 17
Arabic/English book reference : Book 16, Hadith 1424