Al-Adab Al-Mufrad #708

'Abdullah ibn 'Amr was heard to say, "Abu Bakr, may Allah be pleased with him, said to the Prophet, may Allah bless him and grant him peace, 'Teach me a supplication which I can use in my prayer.' He said, 'Say, "O Allah, I have wronged myself greatly. Only You forgive wrong actions. Forgive me with forgiveness directly from you. You are the Ever-Forgiving, Most Merciful."'"