"He 'prays without ceasing' who joins prayer to works that are of obligation, and good works to his prayer.  For virtuous works, or the carrying out of what is enjoined, form part of prayer.  It is only in this way that we can understand the injunction, 'pray without ceasing,' as something that we can carry out; that is to say, if we regard the whole life of the saint as one great continuous prayer."

-Origen, "Prayer"