Sunan Ibn Majah Book 34, Hadith 9
he said to the Messenger of Allah (saas): "Teach me a supplication which I can say during my prayer." He said: "Say: Allahumma inni zalamtu nafsi zulman kathiran wa la yaghfirudh-dhunub illa Anta, faghfirli maghfiratan min 'indika warhamni, innaka Antal-Ghafurur-Rahim (O Allah, I have wronged myself greatly and no one forgives sins but You, so grant me forgiveness from You and have mercy on me, for You are the Oft-Forgiving, Most Merciful)."
"The Messenger of Allah (saas) often used to say: 'Allahumma thabbit qalbi 'ala dinika .' A man said: 'O Messenger of Allah! Do you fear for us when we have believed in you and in (the Message) that you have brought?' He said: 'Hearts are between two of the fingers of the Most Merciful, and He controls them.'" (Hasan)Al-A'mash (one of the narrators) indicated with his fingers.
"The Messenger of Allah (saas) came out to us, leaning on a stick, and when we saw him we stood up. He said: 'Do not do what the Persians do for their leaders.' We said: 'O Messenger of Allah, why don't you pray to Allah for us?' He said: 'Allahummaghfirlana, warhamna, warda 'anna, wa taqabbal minna, wa adkhilnal-jannah, wa najjina minan-nar, wa aslih lana sha'nana kullah. .' It was as if we wanted him to say more, but he said: 'Have I not summed everything for you?'"