Musnad Ahmad 820:0

Narrated to us by Muhammad ibn Ja’far, narrated to us by Shu’bah, from ‘Amr ibn Murrah, who said: I heard Murrah al-Hamadani narrating from Mihjan ibn al-Adra’, that the Messenger of Allah (ﷺ) entered the mosque, and there was a man who had finished his prayer and was reciting the tashahhud, saying: "O Allah, I ask You, O Allah, the One, the Eternal Refuge, who has not begotten and was not begotten, and to whom there is no equivalent, that You forgive me my sins, for You are the Forgiving, the Merciful." The Messenger of Allah (ﷺ) said: "He has been forgiven, he has been forgiven," three times.