Abu Bakr as-Siddiq (RA):
He said to Allah's Messenger (ﷺ), "Teach me a supplication to use in my prayer." He (ﷺ) said: "Say: O Allah, I have greatly wronged myself, and no one forgives sins except You, so grant me forgiveness from You and have mercy on me, You are the Forgiving and the Merciful One."
[Agreed upon].