Musnad Ahmad 30:3550

Rawh ibn ‘Ubadah narrated to us, Shu‘bah narrated to us, from Ya‘la ibn ‘Ata’, he said: I heard ‘Amr ibn ‘Asim ibn Sufyan ibn ‘Abd Allah, he said: I heard Abu Hurayrah saying: "Indeed, the most appropriate supplication is for a man to say: 'O Allah, You are my Lord, and I am Your servant. I have wronged my soul and I have confessed my sin. O Lord, so forgive me my sin, for You are my Lord; indeed, no one forgives sins except You.'"