"Teach me a supplication that I may recite in my prayer." He said: "Say: 'Alahumma inni zalamtu afsi zulman kathiran wa la yaghfirudhunub illa anta faghfirli maghfiratan min 'indika warhamni innaka antalGhafurur-Rahim (O Allah, verily I have wronged myself much and there is None who forgives sins except You. Grant me forgiveness from You and have mercy on me for You are the Oft-Forgiving, Most Merciful.)'"
Sunan an-Nasa'i Book 13, Hadith 124
← Previous Hadith 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.

Sunan an-Nasa'i Book 13, Hadith 123 Next Hadith → "The Messenger of Allah (ﷺ) took my hand and said: 'I love you, O Mu'adh!' I said: 'And I love you, O Messenger of Allah (ﷺ).' Then the Messenger of Allah (ﷺ) said: 'Never forget to say in every prayer: Rabbi a'inni 'ala dhikrika wa shukrika wa husni 'ibadatik (My Lord, help me to remember You, give thanks to You and worship You well.)"

Sunan an-Nasa'i Book 13, Hadith 125