When the Prophet ﷺ finished his prayer with the salutation, he would say, "Allah, forgive me what I have done before and what I will do later, what I have concealed and what I have made public, what I have done in excess, and what You know better than I do. You are the One who brings forward and You are the One who delays. There is no god but You."
كان النبي ﷺ إذا سلم من الصلاة قال: 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.
Abu Dawud (1509) narrated it from Ubaydullah bin Muaz, who said, our father narrated to us, Abdul-Aziz bin Abu Salama narrated to us, from his uncle Majishun bin Abu Salama, from Abdul-Rahman Araj, from Ubaydullah bin Abu Rafi, from Ali bin Abu Talib, and he mentioned it.He also narrated it (761) through another route from Araj with the same chain, at the end of a long hadith, in which it says, and upon finishing the prayer he would say, "O Allah, forgive me for what I have done before..." and he mentioned something similar.It is reported in Sahih Muslim (771:201) that the Prophet ﷺ used to say that between the tashahhud and the taslim, and in another narration, and when he finished the taslim. This may be reconciled by saying that he would sometimes say it between the tashahhud and the taslim, and at other times after the taslim.