Abu Da'ud أبو داود السجستاني الأزدي · The Book of Forgetfulness (In Prayer)

"The Messenger of Allah (ﷺ) forgot and said the taslim after two rak'ahs. Dhul-Shimalain said to him: 'Has the prayer been shortened or did you forget, O Messenger of Allah (ﷺ)?' The Messenger of Allah (ﷺ) said: 'Is Dhul-Yadain speaking the truth?' They said: "Yes." So the Messenger of Allah (ﷺ) stood up and completed the prayer."

"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.)'"