The Enchiridion by St. Augustine
Chapter 71.--The Daily Prayer of the Believer Makes Satisfaction for the Trivial Sins that Daily Stain His Life.
Now the daily prayer of the believer makes satisfaction for those daily sins of a momentary and trivial kind which are necessary incidents of this life. For he can say, |Our Father which art in heaven,| seeing that to such a Father he is now born again of water and of the Spirit. And this prayer certainly takes away the very small sins of daily life. It takes away also those which at one time made the life of the believer very wicked, but which, now that he is changed for the better by repentance, he has given up, provided that as truly as he says, |Forgive us our debts| (for there is no want of debts to be forgiven), so truly does he say, |as we forgive our debtors;| that is, provided he does what he says he does: for to forgive a man who asks for pardon, is really to give alms.