29 But let us grant this also, that the whole year round there may in the fields be found either of tree or of herbs or of any manner of roots, that which may be taken as food uncooked; or, at any rate, let so great exercise of body be used, that the things which require cooking, may be taken even raw without hurt, and people may even in winter weather, no matter how rough, go forth to their fodder; and so it shall be the case that nothing be taken away to be prepared, nothing laid up for the morrow.
Yet will not those men be able to keep these rules, who for many days separating themselves from sight of men, and allowing none access to them, do shut themselves up, living in great earnestness of prayers. For these do use to shut up with themselves store of aliments, such indeed as are most easily and cheaply had, yet still a store which may suffice for those days during which they purpose that no man shall see them; which thing the birds do not. Now touching these men's exercising of themselves in so marvellous continency, seeing that they have leisure for the doing of these things, and not in proud elation but in merciful sanctity do propose themselves for men's imitation, I not only do not blame it, but know not how to praise it as much as it deserves.
And yet what are we to say of such men, according to these persons' understanding of the evangelical words? Or haply the holier they be, the more unlike are they to the fowls? Because unless they lay by for themselves food for many days, to shut themselves up as they do they will not have strength? Howbeit, to them as well as us is it said, “Take therefore no thought for the morrow.”
Source: On the Work of Monks (New Advent)