Authentic Supplication Number 102.

Amongst the final things the Messenger of Allah  would say in the time period between the end of the tashahhud and before the tasleem (120) is: ‘Allahumma ‘ighfirlee ma qaddamtu wa ma ‘akh-khartu, wa ma ‘asrartu wa ma ‘a`lantu, wa ma ‘asraftu wa ma ‘anta ‘a`lamu bihi minnee, ‘antal-muqaddimu wa ‘antal-mu’akh-khiru’, la ‘ilaha ‘illa ‘anta (121).

Footnotes.
(120) The two salutations that end the Muslim’s prayer.
(121) O’ my ‘ilah forgive me what I have set forth, what I have delayed [yet not done], what I have kept secret, what I have made open, what I have acted immoderately in, and what You are more knowledgeable about than I am. You are The Advancer and The Delayer, there is no ‘ilah except You.

Explanation: The Advancer of whatever needs to be advanced, be it verdict or action. He advances what He pleases, and however He pleases. That which He advances is advanced, and that which He delays is delayed. All wisdom is in what He does; even when the wisdom is unknown to us.

Reporters.
Reported by Muslim and is #85 in The Authentic of Good Sayings.