Narrated ‘Abdullah bin ‘Amr:
Abu Bakr As-Siddiq said to the Prophet, “Teach me an invocation with which I may invoke (Allah) in my prayer.” The Prophet said, “Say: Allahumma inni zalamtu nafsi zulman kathiran wala yaghfirudh-dhunuba illa anta, Faghfirli maghfiratan min indika war-hamni, innaka antalGhafur-Rahim.”
Sahih Bukhari, Volume 8, Book75, Number 338