110 During Lent penance should not be only internal and individual, but also external and social. The practice of penance should be fostered in ways that are possible in our own times and in different regions, and according to the circumstances of the faithful; it should be encouraged by the authorities mentioned in Art. 22. Nevertheless, let the paschal fast be kept sacred. Let it be celebrated everywhere on Good Friday and, where possible, prolonged throughout Holy Saturday, so that the joys of the Sunday of the resurrection may be attained with uplifted and clear mind.
Source: Sacrosanctum Concilium (Vatican.va)