Teach me a du'aʿ that I may say in my prayer. He said: ʿSay: O Allah. I have wronged myself greatly and no one forgives sins except You, so grant me forgiveness from You and have mercy on me, for You are the Oft-Forgiving, Most Merciful.ʿ (Using translation from Aḥmad 28)  

أَنَّهُ قَالَ لِرَسُولِ اللهِ ﷺ عَلِّمْنِي دُعَاءً أَدْعُو بِهِ فِي صَلَاتِي قَالَ قُلِ اللهُمَّ إِنِّي ظَلَمْتُ نَفْسِي ظُلْمًا كَثِيرًا وَلَا يَغْفِرُ الذُّنُوبَ إِلَّا أَنْتَ فَاغْفِرْ لِي مَغْفِرَةً مِنْ عِنْدِكَ وَارْحَمْنِي إِنَّكَ أَنْتَ الْغَفُورُ الرَّحِيمُ