LXXIX. To the Petitioners.
If you desire, when praying, to be heard from heaven, break the chains from the lurking-places of wickedness; or if, pitying the poor, you pray by your benefits, doubt not but what you shall have asked may be given to the petitioner. Then truly, if void of benefits, you adore God, do not thus at all make your prayers vainly.
Source: Writings (New Advent)