Midrash su Salmi 31:1

R. Zutra b. Tubia said in the name of Rab: "Repentance is so great, that even when an individual repents the whole world is pardoned together with him, as it is said: I will heal their backsliding, I will love them freely; for my anger is turned away from us. It does not say from them, but from us, — from all of us." What do you call a repentant sinner? When he had an opportunity to do a sin once, and twice, but abstains from committing it. R. Juda, pointing out with his finger, said: "This refers only to when it [the repentance] happened in the same place, with the same person, and at the same time." R. Juda said: "Rab raised the following contradiction: It is written (Pr. 28, 13) He that concealeth his transgressions will not prosper, and (Ps. 31, 1) Happy is he whose transgression is forgiven; whose sin is covered. It presents no difficulty. One refers to a sin publicly known [he ought to confess and repent]; but the other refers to a sin not yet known [he ought to repent before it has become known]." R. Zutra b. Tubia said: "The former deals with sins committed toward a man; and the other deals with sins committed toward God."