Musnad Ahmad 31:168

Yazid narrated to us, Fudayl ibn Marzuq informed us, from Atiyyah al-Awfi, from Abu Sa’id al-Khudri—I said to Fudayl: "Did he attribute it to the Prophet (marfu')?" He said: "I think he did attribute it to the Prophet"—he said: "Whoever says when he goes out to the prayer: 'O Allah, I ask You by the right of those who ask of You, and by the right of this walking of mine, for I have not gone out out of insolence, nor pride, nor showing off, nor for reputation. I have gone out seeking to avoid Your wrath and seeking Your pleasure. I ask You to save me from the Fire and to forgive me my sins, for indeed, none forgives sins except You,' Allah will appoint seventy thousand angels to seek forgiveness for him, and Allah will turn His Face toward him until he finishes his prayer."