Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"If I heard a Hadith from the Messenger of Allah (saw), Allah benefitted me with it as much as He willed, and if I heard it from anyone else, I would ask him to swear me an oath, then if he swore an oath I would believe him. Abu Bakr told me and Abu Bakr spoke the truth that the Messenger of Allah (saw) said: 'There is no man who commits a sin then he performs ablution and does it well, then he prays two Rakah,' (one of the narrators) Mis'ar said: 'then performs prayer and seeks the forgiveness of Allah, but Allah will forgive him.' Sahih