Abu Bakr As-Siddiq said to the Prophet ﷺ "O Messenger of Allah ﷺ! Teach me an invocation with which I may invoke Allah in my prayers." The Prophet ﷺ said, "Say: O Allah! I have wronged my soul very much (oppressed myself), and none forgives the sins but You; so please bestow Your Forgiveness upon me. No doubt, You are the Oft-Forgiving, Most Merciful."
أَنَّ أَبَا بَكْرٍ الصِّدِّيقَ ؓ قَالَ لِلنَّبِيِّ ﷺ يَا رَسُولَ اللَّهِ عَلِّمْنِي دُعَاءً أَدْعُو بِهِ فِي صَلاَتِي قَالَ قُلِ اللَّهُمَّ إِنِّي ظَلَمْتُ نَفْسِي ظُلْمًا كَثِيرًا وَلاَ يَغْفِرُ الذُّنُوبَ إِلاَّ أَنْتَ فَاغْفِرْ لِي مِنْ عِنْدِكَ مَغْفِرَةً إِنَّكَ أَنْتَ الْغَفُورُ الرَّحِيمُ