Nicene and Post-Nicene Fathers: Series II/Volume XI/John Cassian/Conferences of John Cassian, Part I/Conference II/Chapter 26
The answer how we should not exceed the proper measure of food.
Moses: Both duties must be observed in the same way and with equal care: for we ought most scrupulously to preserve the proper allowance of food for the sake of our abstinence, and in like manner out of charity to show courtesy and encouragement to any of the brethren who may arrive; because it is absolutely ridiculous when you offer food to a brother, nay, to Christ Himself, not to partake of it with him, but to make yourself a stranger to his repast. And so we shall keep clear of guilt on either hand if we observe this plan; viz., at the ninth hour to partake of one of the two biscuits which form our proper canonical allowance, and to keep back the other to the evening, in expectation of something like this, that if any of the brethren comes to see us we may partake of it with him, and so add nothing to our own customary allowance: and by this arrangement the arrival of our brother which ought to be a pleasure to us will cause us no inconvenience: since we shall show him the civilities which courtesy requires in such a way as to relax nothing of the strictness of our abstinence. But if no one should come, we may freely take this last biscuit as belonging to us according to our canonical rule, and by this frugality of ours as a single biscuit was taken at the ninth hour, our stomach will not be overloaded at eventide, a thing which is often the case with those who under the idea that they are observing a stricter abstinence put off all their repast till evening; for the fact that we have but recently taken food hinders our intellect from being bright and keen both in our evening and in our nocturnal prayers, and so at the ninth hour a convenient and suitable time has been allowed for food, in which a monk can refresh himself and so find that he is not only fresh and bright during his nocturnal vigils, but also perfectly ready for his evening prayers, as his food is already digested.
With such a banquet of two courses, as it were, the holy Moses feasted us, showing us not only the grace and power of discretion by his present learned speech, but also the method of renunciation and the end and aim of the monastic life by the discussion previously held; so as to make clearer than daylight what we had hitherto pursued simply with fervour of spirit and zeal for God but with closed eyes, and to make us feel how far we had up till then wandered from purity of heart and the straight line of our course, since the practice of all visible arts belonging to this life cannot possibly stand without an understanding of their aim, nor can it be taken in hand without a clear view of a definite end.