Mishkat al-Masabih 886

Abu Bakr as-Siddiq said that he asked God’s Messenger to teach him a supplication to use in his prayer, and he told him to say, “O God, I have greatly wronged myself, and Thou alone canst forgive sins, so grant me forgiveness from Thee and show mercy to me. Thou art the forgiving and the merciful One.” (Bukhari and Muslim.)