Hisnul Muslim · Dua 57 of 267
Invocations after the final Tash-ahhud and before ending the prayer
((اللَّهُمَّ إِنِّي ظَلَمْتُ نَفْسِي ظُلْماً كَثِيراً، وَلاَ يَغْفِرُ الذُّنوبَ إِلاَّ أَنْتَ، فَاغْفِرْ لِي مَغْفِرَةً مِنْ عِنْدِكَ وَارْحَمْنِي، إِنَّكَ أَنْتَ الغَفورُ الرَّحيمُ)).
How to read it
Allahumma innee thalamtu nafsee thulman katheeran wala yaghfiruth-thunooba illa ant, faghfir lee maghfiratan min AAindik warhamnee, innaka antal-Ghafoorur-Raheem.
English meaning
O Allah, I have indeed oppressed my soul excessively and none can forgive sin except You, so forgive me a forgiveness from Yourself and have mercy upon me. Surely, You are The Most-Forgiving, The Most-Merciful.)(From Yourself: i.e. from Your innermost grace without deserving it and a forgiveness which is befitting to your tremendous generosity.