Here is the reference from the Council of Trent:
CONCERNING INDULGENCES
THIRD DECREE
On the fourth day of December.
Whereas the power of conferring Indulgences was granted by Christ to the Church; and she has, even in the most ancient times, used the said power, delivered unto her of God; the sacred holy Synod teaches, and enjoins, that the use of Indulgences, for the Christian people most salutary, and approved of by the authority of sacred Councils, is to be retained in the Church; and It condemns with anathema those who either assert, that they are useless ; or who deny that there is in the Church the power of granting them. In granting them, however, It desires that, in accordance with the ancient and approved custom in the Church, moderation be observed; lest, by excessive facility, ecclesastical discipline be enervated. And being desirous that the abuses which have crept therein, and by occasion of which this honourable name of Indulgences is blasphemed by heretics, be amended and corrected, It ordains generally by this decree, that all evil gains for the obtaining thereof,-whence a most prolific cause of abuses amongst the Christian people has been derived,-be wholly abolished.