Teshuva in Responsa VIII
In another Responsum, Rabbi Isaac Trani considers the question of penance.: A certain man enjoyed a good reputation in the community. One day he came to the court entirely of his own accord and confessed that he had been guilty of all three capital sins; he had been a highwayman and had killed his victims; he had seduced married women; and he had denied God. Rav Trani was asked whether repentance is possible for such a severe sinner and, if it is, what penances should be imposed on him.
Rav Trani answers that the criminal cannot bring back to life those he has murdered and he cannot rescue his children borne by the married women from the taint of bastardy. In this sense his repentance is of no avail.
But so far as he himself is concerned, he is capable of repentance. His penance must consist in realizing three separate ideas. He must repent sincerely, he must suffer much, and he must do good deeds.
He must confess his sins publicly, except for the sins with the married women (which must be kept secret to avoid harming their reputation and that of their children).
As for suffering, he should know that God will punish him, but, in addition, he himself must engage in self-torment. He should fast for many a day. Even though the Rabbis say that one who fast is a sinner, this does not apply to one who fasts as atonement for sin.
He should also go into exile from his home.
As for the question whether he should fast even on the Sabbaths and festivals, the answer is no. It will be even more painful for him if he has to revert to fasting after having enjoyed food on the Sabbath.
Even if, as a result of his fasts, he is forced to study less than he would were he to eat, he should still fast.
Furthermore, the very fact that, as a scholar, he is unable to study will itself be a form of mortification. At first he should study only passages of rebuke in Scripture and the like, just as a mourner does. But after thirty days he can study whatever passages in the Torah he so desires.
As for exile, since he committed the three capital sins, he should go to three different towns, spending a year in each.
After all this, he should eat only bread and drink only water. On Sabbath and festivals he can eat a little meat. He should never attend a banquet. As for deeds, he should do ‘heaps and heaps of good deeds’.
He should help others, and buy books to lend to scholars. He should return unto the Lord and He will have mercy upon him, and to our God, for He will abundantly pardon.