Supplication after remembrance

Hanzalah bin 'Ali narrated that: Mihjan bin Al-Adra' narrated to him that the Messenger of Allah (ﷺ) entered the masjid and there was a man who had finished his prayer and he was reciting the tashahhud. He said: "Allahumma inni as'aluka ya Allah! Bi-annakal-Wahidul-Ahad us-Samad, alladhi lam yalid wa lam yowled, wa lam yakun lahu kufuwan ahad, an taghfirali dhunubi, innaka antal-Ghafurur-Rahim (O Allah, I ask of You, O Allah, as You are the One, the Only, the Self-Sufficient Master, Who begets not nor was He begotten, and there is None equal or comparable to Him, forgive me my sins, for You are the Oft-Forgiving, Most Merciful.)" The Messenger of Allah (ﷺ) said: "He has been forgiven," three times.