It is therefore a holy and wholesome thought to pray for the dead,that they may be loosed from sins."--2 Machabees 12:46
The Council of Trent told us "That there is a Purgatory and that the souls there detained are assisted by the most acceptable sacrifice of the altar."
Invocation for the Holy Souls
(Indulgence of 300 days, applicable only to the holy souls. (582)
Our Father, Hail Mary, Eternal rest, etc. (Indulgence of 500 days. (596))
(The Roman Missal)
A Prayer for the Souls in Purgatory