Sunan Ibn Majah

It was narrated from Abu Bakr Siddiq that :he said to the Messenger of Allah (saas): ""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)