Abu Dawud Book 2, Hadith Number 1405.

Narated By Ali ibn Abu Talib : When the Prophet (PBUH) uttered the salutation at the end of the prayer, he used to say: “O Allah, forgive me my former and latter sins, what I have kept secret and what I have done openly, and what I have done extravagance; and what Thou knowest better than I do. Thou art the Advancer, the Delayer, there is no god but Thou”