Thomas Aquinas

“ Secondly, penance is taken as a virtue, and in this way its act consists in the detestation of evil done, together with the purpose of amendment and the intention of expiating the evil, or of placating God for the offense committed. Now detestation of evil befits a person according as he is naturally ordained to good. ”

“ Now the devils are exceeding evil, nor is there any punishment that they lack. Therefore they can repent.
Objection 3: Further, a thing is more easily moved to that which is according to its nature than to that which is against its nature: thus water which has by violence been heated, of itself returns to its natural property. Now angels can be moved to sin which is contrary to their common nature. Much more therefore can they return to that which is in accord with their nature. But this is done by penance. Therefore they are susceptible to penance. ”

“ Further, we read in the Lives of the Fathers, that one of them said that even Abraham will repent of not having done more good. But one ought to repent of evil done more than of good left undone, and which one was not bound to do, for such is the good in question. Therefore repentance will be there of evil done. ”

“ Although the innocent have committed no sin, nevertheless they can, so that they are competent to have the habit of penance. Yet this habit can never proceed to its act, except perhaps with regard to their venial sins, because mortal sins destroy the habit. ”

“ And because removal of the matter entails the removal of the act, since there can be no act without the matter into which it passes, hence the habit of a virtue is possible in one for whom the matter is not available, for the reason that it can be available, so that the habit can proceed to its act---thus a poor man can have the habit of magnificence, but not the act, because he is not possessed of great wealth which is the matter of magnificence, but he can be possessed thereof. ”

“ And since this order or inclination is not entirely destroyed in any creature, it remains even in the damned, and consequently the passion of repentance, or something like it, remains in them too, as stated in Wis. 5:3 " (saying) within themselves, repenting," etc. ”