Paulinus of Milan

Indeed, to the penitent confession alone does not suffice, unless correction of the deed follows, with the result that the penitent does not continue to do deeds that demand repentance. He should even humble his soul just as holy David, who, when he heard from the prophet, "Your sin is pardoned," became more humble in the correction of his sin, so that "he did eat ashes like bread and mingled his drink with weeping."