Jābir radhiyallāhu ‘anhu narrates that once a person came into the company of the Prophet sallallāhu ‘alayhi wasallams and said, “My sins, my sins!” So the Prophet sallallāhu ‘alayhi wasallam said to him, “Say:

Allāhumma maghfiratuka awsa‘u min dhunūbī,
wa rahmatuka arjā ‘indī min ‘amalī

O Allāh! Your forgiveness is vaster than my sins,
and your mercy is more encompassing to me than my good deeds.”

So the person said the words taught to him, and then the Prophet sallallāhu ‘alayhi wasallam told him to repeat them thrice, which he did. Thereafter the Prophet sallallāhu ‘alayhi wasallam said, “Go, for verily Allāh has forgiven you!”

[Al-Hākim & Al-Bayhaqī]