Reference : Hisn al-Muslim 58

اللّهُـمَّ اغْـفِرْ لي ما قَدَّمْـتُ وَما أَخَّرْت ، 
وَما أَسْـرَرْتُ وَما أَعْلَـنْت ، 
وَما أَسْـرَفْت ، وَما أَنْتَ أَعْـلَمُ بِهِ مِنِّي . 
أَنْتَ المُقَـدِّمُ، وَأَنْتَ المُـؤَخِّـرُ 
لا إِلهَ إِلاّ أَنْـت
Allāhummagh’fir lī mā qaddamtu, wa mā ‘akhkhartu, 
wa mā ‘asrartu, wa mā ‘a`lantu, 
wa mā ‘asraftu, wa mā 'anta ‘a`lamu bihi minnī.
‘anta ‘l-Muqaddimu, wa 'anta ‘l-Mu‘akhkhiru 
lā 'ilāha 'illā 'anta.


O Allah, forgive me what I have sent before me and what I have left behind me, 
what I have concealed and what I have done openly, 
what I have done in excess, and what 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.

Reference:
Muslim 1/534.

Chapter: After the last tashahhud and before salam