It was narrated from Abu Bakr Siddiq (RA) that: he said to the Messenger of Allah (peace be upon him): “Teach me a supplication which I can say during my prayer.” He said: “Say: Allahumma inni zalamtu nafsi zulman kathiran wa la yaghfirudh-dhunub illa Anta, faghfirli maghfiratan min ‘indika warhamni, innaka Antal-Ghafurur-Rahim (O Allah, I have wronged myself greatly and no one forgives sins but You, so grant me forgiveness from You and have mercy on me, for You are the Oft-Forgiving, Most Merciful).”
Sunan Ibn Majah, Book 34, Hadith 9
